Hey, sorry for the late reply, my work hours are killing me right now, most of the stuff i actually found out by experimenting myself. Luckily i knew blender before i got into sims 4 modding, so it was an easy transition for me.
All you need to get is Sims4Studio and you are pretty much set, the program is super intuitive, so it's easy to figure out. As long as you know how to do 3d modelling, you'll be pretty much making stuff fairly quickly.
I personally don't know *that much* about sims 4 modding, and there is a lot that can be done still. So i could only reccomend checking some video tutorials or visiting the official sims4studio forums and check some guides over there.