Hello all
I've started modding the sims 4 for my own game (no sharing yet) pretty recently (already modded some easier games before though), I've done some basic changes such as changing the mood buff aliens receive for being discovered. Have also been a bit deeper into modifying a few aspects of a complex mod I have installed (the main mod isn't mine, I've just been into the complex files to make some changes about it for me only).

But here is the main point, I have this idea about creating a whole new life state that would fit perfectly for one of my save, I know it would be a complex life state if I got to do everything I have in mind for it but I plan to extend it step by step as I get more skilled and learn how to do more for it.
The problem is, I don't know how to start from scratch to mod a life state. Which files do I have to use and edit to start with ? Which tools can/should I use for it ?
To help you know what I have in mind, and help me the best way you can, here is what I'd like to achieve as a starting point : I would like to have my life state made on the base of the alien one but without the dual form (only human like looking) and have mixing features with spellcasters. Is that even possible ?

I know I am still a beginner at modding, and perhaps I've got a very ambitious goal, but whatever, I'm only doing it for myself anyway for now, so I can big dream without harming anyone
So I'm not here to receive the kind of answers that just point out I'm a bigger, but I'm looking for real answers to my actual question, no matter how hard and complex the process of modding this life state will be

Thanks in advance for those who would at least take the time to read me so far and think about my issue.

Occults are just traits so anyone can make one, but the problem lies in the fact that it will never truly be considered a new occult because you can't just add one into EA's system, that stuff is pretty much hardcoded (no one has successfully added to it, they've tried). So this means choosing it in CAS, dual forms, the general UI, unique stuff like the vampire perks and spellbook, etc.

But basically you just find an existing occult trait to use as a base. In your case the alien and spellcaster. Make it custom, then just add on to it by creating interactions, buffs, etc. that fit. That's pretty much it. I'm not sure what you want from spellcasters but if it's the spells you should be able to give them access to the spellbook. Don't know the specifics but I know it's possible based on the Vampire Witches mod, etc.

As for tools, either Mod Constructor (limited but easier for beginners making custom projects) or Sims4Studio (no limits but harder for beginners).
Here's a bunch of resources:

Thank you for your helping reply.
Yes, that's basically it, as a starting point I would like to have an alien who's true form looks like humans (so no disguise available/needed and related interactions) and who can also be a spellcaster, so this sim would have full access to all alien and spellcaster related interactions, have the charge need, and access to the spellbook and spellcaster's perks. As of in the future I would also try to add some new custom interactions to this life state and maybe try to delete some from alien and spellcaster that I would find less relevant for it.

So how do I start ? Which specific files from the life sates I want as a base do I need to find and custom ? And how ?

I've got both Mod Constructor and S4S, as well as Notepad++.
I'll have a look to every links you've posted too, thank's a lot.

Hi, sorry for the late reply, were you able to get started since we last spoke?