1. How many bedrooms does a typical house in your hoods have? Do you have many families living together, or do they tend to get their own home?
I usually use houses that come with the game, either in the bin or neighborhood already. Sometimes i'll download a home. I'll make homes at times when I can't find one to suit the family or within their budget. Bedrooms depend on the number of sims. A couple will of course share a bedroom and kids may get their own room if they have enough space/money. I always try to have any babies and toddlers in their own room so as not to wake any sims I don't want them to...or each other. If they must share a room though they must. Usually a family will have their own home but sometimes they will live together depending on the sims and how many kids each family will have, and only if they are friends.
2. How many bathrooms do you normally have? How does adding Sims change your opinion on how many bathrooms are needed?
Depends on the house as usually I don't build it myself, and the number of sims. The less sims the less bathrooms they can get away with, if they are rich they may have a bathroom for each bedroom and then some..if they are poor they may not get as many bathrooms as they would like.
3. What other rooms do you add to your houses, aside from bedroom, bathroom and kitchen?
Living room, sometimes a dining room. Depending on family and wealth they may get a study, a play room..
4. Do you have any non-traditional rooms, like a hobby room or a play room?
Depending on the family I may add a hobby or play room.
5. Do you use a lot of CC to make room types that EA never intended, like a garden shack or something such?
No.
6. Are there any must have items, aside from the obvious (bed, toilet, fridge etc) that you tend to have in most homes?
Burglar alarm, fire alarm, sim modder for usually just changing LTW, batbox to clean stuff up, InSim budget thing...to take away money they didn't earn according to me. Other than that no.

1. How many bedrooms does a typical house in your hoods have? Do you have many families living together, or do they tend to get their own home?

Obviously depends on the amount of sims in the household, but since I play big families (8-25 sims), there are usually several bedrooms. In my simself's house there are seven. Normally there are at least three or four bedrooms, since every couple has one (and there are usually at least two or three couples), and then the kids usually share a room or two, depending on the house layout. Boys and girls are mixed. I rarely play small families (under 8 sims), they bore me... and to me family is extremely important, so my adult sims tend to share houses with at last one sibling or more, and their spouses and offspring (and parents and grandparents and...). My simself's spouse has six brothers, they all live with us, and then there's the spouses and kids of those, and almost always other guests staying the night (usually cousins and aunts and uncles and stuff), so the house is filled to the brim, and there's a lot of things happening 24/7.

2. How many bathrooms do you normally have? How does adding Sims change your opinion on how many bathrooms are needed?

One or two, depending on how many floors there are in the house. Always one on the ground floor, and then another if there's a second floor. My bathrooms are really big though, at my simself's house there are 6 toilets, 2 showers and 2 bathtubs in one bathroom. I have the "no privacy" hack, so all my sims use the bathroom together, I can have two sims taking a bath, two showering, and several on the can reading the newspaper at the same time (and others just hanging out and playing and stuff ). This is how we live at home IRL, so it's natural to me.
Guests also get to use the showers. Especially the naughty one is very popular. :P

3. What other rooms do you add to your houses, aside from bedroom, bathroom and kitchen?

A living room, which often is a living room-dining room-kitchen-combo, open concept. Usually also an office/study/library type of room...

4. Do you have any non-traditional rooms, like a hobby room or a play room?

Rarely. Everybody tends to hang out in the living/dining/kitchen combo anyway, when they're not sleeping. I have the instruments and other hobby items in the same space.

5. Do you use a lot of CC to make room types that EA never intended, like a garden shack or something such?

Rarely.

6. Are there any must have items, aside from the obvious (bed, toilet, fridge etc) that you tend to have in most homes?

Batbox, SimBlender, College Adjuster, ACR adjuster, Visitor Controller, Weather Controller, Teleporter cat. I never ever have a house without all of these. A fire alarm, both inside and outside, and a sprinkler above the stove (and fireplace, if there is one). No burglar alarms, since I just zap the burglar away with the Teleporter cat the second he or she appears on the lot.
Usually everybody gets a stereo (the white, basic one, I don't like the huge ones), since my sims tend to be very musical. Piano and/or synth... computer (the Pear ShinyStation, the color varies depending on the family "preference"). Many have the ballet barre. Everybody has a bookcase or several, and most have (the cheaper) telescope. Again, I don't like the big one.
Many houses have the naughty shower.

This thread would seem to lend itself to pictures

What is average? My Sims' houses vary from the tiny downtown starter homes in Mendoza Lane to the Summerdreams' palace. Small is probably more typical. Only the original 3 pre-made Veronaville families live in really big houses. The exception is Craig Royce (the Slob), who lives in a big downtown town house, but that is really hostel-type accommodation for former townie teens; Craig is the warden.
1. How many bedrooms does a typical house in your hoods have? Do you have many families living together, or do they tend to get their own home?
It depends upon the house and who lives in it. The smallest houses have one bedroom, others have two or more. Nearly all my Sims live in Maxis houses, but some of them are extensively rebuilt. Conventional families have their own house, but single Sims, including quite a few teens, often share. Unlike Nysha's, mine usually get on well together -- Jamie Siddons and Jihoon LeTourneau even share a bed, although there is no romantic relationship between them. In "normal" families children, including teens, often share a room, but my siblings usually get on well together -- friendly hugs and family kisses are commonplace. Teens living in Craig Royce's Teen Townie Hostel usually get their own room, but the furnishings are standardised and rather "institutional". In time they may personalise their rooms.

2. How many bathrooms do you normally have? How does adding Sims change your opinion on how many bathrooms are needed?
One or two is normal, but some larger houses have more. The Corntons have got 3 bathrooms and a downstairs toilet, which is a lot for a family of four, but theirs is an unusual family. They often have overnight guests. The two large bedrooms in their converted garage have en-suite bathrooms.
3. What other rooms do you add to your houses, aside from bedroom, bathroom and kitchen?
Many of the Maxis houses are open-plan, but most have rooms (or areas) for living and dining.
4. Do you have any non-traditional rooms, like a hobby room or a play room?
The Rev. Elspeth Anderson has a study and a tiny TV room in her Rectory. The Corntons have a chess room(!), but that is really because the upstairs rooms at 103 Custer Boulevard are too small to be practical bedrooms. I couldn't work out how to fit a double bed into any of them. For a while the boys slept in a double bed downstairs, but quite soon they converted the garage into a love nest. (Father and both boys are all Romance.) When Audrey moved in, they added a second storey above the old garage. A couple of my Sims have garden sheds. Martin Moltke uses his for exercise machines and storage; Joe Lambert grows 8 money trees in his! Harry Hastie and Dean Cameron keep their money trees in a locked room inside the house, which Dean's mother also uses for painting. (Other Sims keep money trees in their bedrooms -- the idea is always to keep the room locked so non-residents can't take the money!) In the Teen Townie Hostel there is a games and activities room with a dart board, a computer, a couple of easels and a piano. There is a plan to convert the garage into a bigger games and activities room, and turn the existing one into an additional bedroom.
5. Do you use a lot of CC to make room types that EA never intended, like a garden shack or something such?
Not really. My garden sheds are built with Maxis walls, doors, windows and roofs, and most of my furniture is Maxis or similar.
6. Are there any must have items, aside from the obvious (bed, toilet, fridge etc) that you tend to have in most homes?
Despite having Squinge's No More Fires hack, I still put a fire alarm above/beside very cooker and fireplace. (Call me a pessimist!) Neder's Variable Meal Servings (which looks just like a second fire alarm) is now a standard fitting in all my houses too. Many houses also get the Sim Manipulator and / or Inge's Teleporter Plus painting. These tend to be added as needed. I too like a wardrobe in every bedroom, and sometimes one in the living room too. For this purpose I often use ChristianLov's Sim Boutique Clothing Rack or one of Merola's one tile dressers (here and here). If there are teens in the house, they usually eventually get ChristianLov's Easy Bed. I don't usually let them woohoo, but I find it a bit ridiculous that they can't even kiss and cuddle in a Maxis bed, when they can make out so wildly on the sofa!

[EDIT] Added pictures as egswanso suggested. I too use ChristanLov's No Privacy in bathrooms hack so one Sim can use the shower while another uses the toilet.

I didn't know there was a no more fires hack that existed. I was in a terrible fire last year, lost home, pets, everything and almost my life too. I googled it and found it. I know that wasn't the point of the post but thank you none the less! :D

1. How many bedrooms does a typical house in your hoods have?
The Cookie Cutter homes usually have two stories per house and are simply painted different colors. Upstairs, three bedrooms. Master Bed, Child bed, Second Bed (usually where the Humble computer lives.)
The "Expandable" homes (that would evolve gradually and based on family funds, like a legacy house usually does) vary family to family in bedroom numbers. A minimum of 1 and a maximum of 20.

2. Do you have many families living together, or do they tend to get their own home?
Depends on the family and what goals I have for them. Grandparents who are family sims with wants to see grandchildren are often invited to live in with their children, but most sims get their own house.

3. How many bathrooms do you normally have? How does adding Sims change your opinion on how many bathrooms are needed?
In the Cookie Cutter homes, four. Upstairs, the Master bath hooked on to the Master bed. Across from bedroom 2 + 3 is a full bath designed with children in mind. First floor has a half-bath. Garage has a walled in toilet, the sink is usually outside of the bathroom (sometimes referred to as a quarter bath).
Adding sims doesn't much change how many bathrooms are needed in cookie cutter homes because I adhere to a strict "3 kids max" for those families. The bathroom set up is sufficient for all bladders involved. :P

In the "Expandable" homes, a minimum of 1 and a maximum of 10. Sizes will vary.
"Expandable" homes are often expanded as families grow, but usually number less than 6 by the end of the developmental phase.

4. What other rooms do you add to your houses, aside from bedroom, bathroom and kitchen?
Cookie Cutter homes have a living room, a romper room (second living room), a dining room, a garage and a fenced in backyard.
"Expandable" homes vary.

5. Do you have any non-traditional rooms, like a hobby room or a play room?
That would be what a romper room entails. The romper room usually features games like Majong or Don't Wake The Llama. Pool is a favorite passtime with older families.
"Expandable" homes ..... vary! :P

6. Do you use a lot of CC to make room types that EA never intended, like a garden shack or something such?
No. The only building CC I have is a stair-wall fix, and it doesn't even get used much because I play with walls down.

7. Are there any must have items, aside from the obvious (bed, toilet, fridge etc) that you tend to have in most homes?

Every home gets the ACR spawned object, a bat box and Phaenoh's phonebook. The telephone is always placed within two grid squares of the front door. Other than that? No.

1. How many bedrooms does a typical house in your hoods have? Do you have many families living together, or do they tend to get their own home?

2 or 3 bedrooms depending on family size - even when I had a sim with 6 children they all doubled up (thank you for ts3 bunck bed conversions!)
I did have multiple families living together when I simulated apartments and duplexes before I got AL expansion. Not so much anymore. Single sim, elder sim, or a childless couple go the apartment route and those who intend on starting families get their own home.

2. How many bathrooms do you normally have? How does adding Sims change your opinion on how many bathrooms are needed?

1-2. For big families though I tend to lean for the 4-bathroom place, a half-bathroom is always a friend on a big household!

3. What other rooms do you add to your houses, aside from bedroom, bathroom and kitchen?

Usually a den, or computer room, game room, or study - a living room/common space. Sometimes if they are fancy, they get a dining room. Music rooms I have done before for either pianos/violins or a full band set for practice.

4. Do you have any non-traditional rooms, like a hobby room or a play room?

Sometimes I go for nurseries if there's more than one kiddo toddling around. Hobby rooms are rare since I haven't had free time for that long.

5. Do you use a lot of CC to make room types that EA never intended, like a garden shack or something such?

I did modify a house so the outside deck was a greenhouse - used no CC at all. But I can't say that i have.

6. Are there any must have items, aside from the obvious (bed, toilet, fridge etc) that you tend to have in most homes?

Cappuccino machine- to keep sims sleeping schedules balanced. Chess board is another - Between that and the telescope for logic points (and not having to fill out 10 crossword puzzles from the newspaper to gain logic) - it fits better in most houses.

I use predesigned floor plans from the web, because I suck at creating houses myself (giant boxes...). The size of the house varies based on the social class of the household (I play a modified Warwick challenge, although I haven't played in several months because I just had twins).

1. How many bedrooms does a typical house in your hoods have? Do you have many families living together, or do they tend to get their own home?
It varies, from one bedroom in the tiniest homes, to several in the larger homes. If that's not enough for the people on the lot, tough cookies. I usually only have one family in one home or apartment, although that can include extended family like uncles and whatnot who never moved out.

2. How many bathrooms do you normally have? How does adding Sims change your opinion on how many bathrooms are needed?
Again, I just follow the floor plan. If an 8 member household ends up with one bathroom, tough cookies. Yes, I am tough on my sims.

3. What other rooms do you add to your houses, aside from bedroom, bathroom and kitchen?
Larger floor plans tend to have breakfast nooks, walk in closets, family rooms or great rooms, garages, etc, which I follow.

4. Do you have any non-traditional rooms, like a hobby room or a play room?
In floor plans with a breakfast nook and a dining room, I find that the dining room is a good location for a study/homework area, usually being very close to the front door. Walk in closets are good nurseries. Sometimes I turn the garage into a greenhouse.

5. Do you use a lot of CC to make room types that EA never intended, like a garden shack or something such?
No.

6. Are there any must have items, aside from the obvious (bed, toilet, fridge etc) that you tend to have in most homes?
If they can afford it, and there is room, I try to start out with a little something from each category of hobby/party/etc items, so a bookshelf, an instrument, a game, etc. This ends up covering all skilling requirements, and adds a few sources of fun. I add to these over time based on wants only - so I'm not going to add, say, a bubble blower until someone rolls that want.

1. How many bedrooms does a typical house in your hoods have? Do you have many families living together, or do they tend to get their own home?
I don't keep multiple families in one home, so the regular house in my hood would have 1 master bedroom, 1-2 rooms for the kids and 1 guest bedroom. Sometimes, the grandparents may live in - they either use the spare bedroom or have a room of their own (depending on the lot size).

2. How many bathrooms do you normally have? How does adding Sims change your opinion on how many bathrooms are needed?
My rule is to have at least 1 bathroom per sim in household. However, if a new sim is born in the family, they might share a bathroom with their brother/sister. Again, if I marry one of the household sims and the spouse moves in, the couple will share a bathroom.

3. What other rooms do you add to your houses, aside from bedroom, bathroom and kitchen?
My houses usually have a family room (living + dining) and a study/library apart from the basics. Depending on the sims profile and hobbies, I could add either a game room, fitness space, sauna or arts studio.

4. Do you have any non-traditional rooms, like a hobby room or a play room?
Yep - arts studio, gym, game rooms.

5. Do you use a lot of CC to make room types that EA never intended, like a garden shack or something such?
Not really. I might have a laundry room tho.

6. Are there any must have items, aside from the obvious (bed, toilet, fridge etc) that you tend to have in most homes?
Fire and burglar alarms are a definite must-have. Other basics include computer, TV, phone, bookcase, bathroom mirror...

My neighborhood generally draws from pre-industrial society for inspiration, so every home begins with a garden. Every house is built around its fireplace; while my Sims can't use them for cooking (and the cooking fireplace available here is not useful, as it only gives 1 hunger point), the fireplace is usually in the same room as the kitchen or shares the wall with it. I typically combine the kitchen, dining, and 'family' areas into one Great Room, or have a kitchenish nook and a Great Room. Bookcases are a requirement, and if they can afford it, so are painting easels, chess sets, and a musical instrument of some kind. My sims do not have TVs and do not have computers. If the house is associated with a powerful sim, there's usually a large private study for him or her. Invariably the children want to plop their homework in here, which ruins the private domain feel. Multigenerational families are the norm in my neighborhood, I often combine young couples in one house, and I sometimes pull teenagers out of crowded houses to be nursemaids/attendants in other households. I almost always have a front porch. There usually one bathroom per floor, near the kitchen; the upstairs bathroom will be directly above the downstairs bathroom, on the same wall as the kitchen because obviously they share common pipes in the wall. I don't have to do that with wiring because my sims all use candles and gas lamps.

1. Family homes (mum, dad, children) usually 3 bedroom, also depends on the number of children in the family. I don't like having more than two Sims to a bedroom- feels chaotic. I rarely have other relatives living with the family unless i made them in CAS, but then I found that I usually get rid of them in the end? I've only got/ had 1 successful large family in game..its hard.
2. Number of bathrooms depends on the size of the house, sometimes on the number of Sims. Generally 1 or 2 bathrooms and an extra wc, usually by the front door.
3. Entryways/ hallways! I hate it when the front door opens straight into the living room. I usually make living/diners, sometimes kitchen diners, rarely open floor plans. If there isn't any space within the house for any creative activities, i like to build a pretty extension and make it slightly different to the rest of the house, and the usually add a piano, games set etc.

4. Generally no, but as in #3 an extension is added, so I guess a hobby room, only if there is not enough space within the house and its too much ef to redo a certain room or something
5. Other than the TS2 store stuff, no actually. I have a few wall papers that I downloaded from here, but thats about it.
6. Pianos, end tables, MIRRORRS- i love them,they reflect stuff! and general maxis made stuff that makes houses look better. I generally build and add stuff until it feels like home to me

Does this satisfy your curiosity? :D