So, I want to put outfits I've made for character models I modeled from TV shows (Last Airbender, Legend of Korra, Steven Universe to name a few) I've created as well as outfits ripped from games like Dead Or Alive, Mass Effect and RWBY GE into Sims 3/Sims 4. I've found a tutorial that explains the process, but the 3D software it asks for you to use is Milkshape 3D.

I've downloaded most of the the following programs that the tutorial requires (CAS Unitool, The Sims Workshop, Milkshape 3D and a couple others I can't remember the names of right now), but is there a tutorial that deals strictly with a Blender 2.7+ workflow? Also, how do I find the body meshes from the game I can weight my outfits to?

Basically, I need a bit of help

Here's a link to my imgur gallery if you want to see the outfits and other models I make.

http://andywilkins.imgur.com/all/

I don't know if this is what you looking for, but here is tutorial how to convert clothes from other games to sims 3 -https://www.youtube.com/watch?v=jqPWXfeNT0U. Basically, if your mesh is fine, you just have to adjust it to sims 3 body in milkshape, make textures and using such programs as TSR Wokshop make proper format for ts3.

I'd say Blender is the best tool for advanced meshing in TS3. Get the plugins, then go from there. .GEOM files are used by S3PE, your go-to tool for modding resources.
Small side-note: I personally use Milkshape for simple mesh edits, plugins here, because Blender sometimes has compatibility issues with the GEOM tools.

Well... Actually you can use any 3D modeling program, but you don't have to use Milkhape for meshing at all! Blender's plugins (At least for me) Never have seemed to have worked at all. And I've tons of plugins installed for blender :P
I would suggest, when following tutorials/converting tutorials to basically do this:

- Meshing part/making it fit the ts3 body: Any 3D modeling program you own/prefer
- when done, export it as a OBJ, and reimport it into milkshape 3D. There you want to fix the neck seams and ankle sims.

There are 2 ways to make clothing for ts3 though (I guess for ts4 you want to visit the ts4 creator forums ^-~) There's the CTU way, which if you want to use CTU, you really do want to get the stuff Grijzepilion mentioned and check out this CTU tutorial: http://www.modthesims.info/showthread.php?t=397260

Or you can always use TSRW (Please get this one instead, the latest ones are really buggy with ts3: http://greenplumbboblover.tumblr.co...56/fix-tsrw-195 )
For a TSRW casting tutorial, you can check out my video tutorial right here, I also made a conversion video (DAI to ts3) which you can find on the same channel though, if you prefer those.: https://www.youtube.com/playlist?li...f6SdjhTA383CbKH
This is also a really great TSRW tutorial: http://wiki.thesimsresource.com/ima...ng_Tutorial.pdf

Yeah, so about that, how the hell do you get Blender to work with TS3? I kinda need it for some mesh edits that I've been wanting to do for...I dunno, a year. By "kinda need", I mean "literally no other way to get it done".

Hmm well there are ways around, like using FBX because it supports the bones. Unless you're working on a default replacement? With those I usually import the mesh into TSRW, export it as a package, and export all the BGEO, GEOM and replace them with the default replacement package that you cloned with s3oc. I do remember someone being able to import/export their meshes with ts3 pose tool for blender. I haven't really looked into that yet though.

FBX you say? So hwat do I use to convert the GEOM to FBX before I open the FBX in Blender? Will Milkshape do?

So, in that case how do I import the Sims 3 bodyshapes with their weights intact? Will the GEOM plugin do that just fine? Modelling and texturing the clothes isn't a problem for me, its more that I want to be able to weight the clothes in Blender if at all possible before exporting to Milkshape.

That's something that this tool called mesh toolkit will do for you: http://modthesims.info/d/481950
Keeping the bones weights I mean. This entire progress is entirely different for the sims 4 though! Because then you're basically forced to use Blender instead.

Anyway, the way to add the bones and morphs to it are all explained in the tutorial I linked. Here are the body references: http://modthesims.info/t/411795

@grijzepilion

Well, basically you import the GEOM file (IF the plugins are working for you of course ) and export it as a FBX into Milkshape to keep the bones. You'll be able to get it back into Blender with it's bones attached to it as well. but the entire progress is kind of a workaround though ^- ~