Sorry guys, especially Ronin1973, I took some stuff in the wrong way and I should not have, my answer was dumb so I apologize. And thanks for your reply.
I built the systems in the original post by trying to follow a general template I found in most semi modular synths and pre made systems by various manufacturers I could found online. Stuff like 0-coast, mother 32, templates by reverb.com, perfect circuit 54hp and east/west coast series. That's why I had the feeling I had most of the modules I needed for them to work, or covered those that weren't there somehow, but obviously I missed some.
Also, I really want to focus on exploring a limited number of modules instead of allowing myself future expansions, if that makes sense. That's why I feel like only going for 3u of carefully picked modules would work better for me than buying a big case right away. I really like the idea of working within creative restrictions instead of allowing myself to buy more if I want to. It would also allow me to focus on the music while still having a very powerful tool to make cool sounds and experiment.
Moreover, 3u would fit on my desk, 6u would not, so in a way, I would use it much more if I keep it on the smaller side. I really believe that a few oscillators/modulators can already bring many exotic functionnalities compared to what I can do at the moment with what i have.
Anyway, sorry and thanks again. I think I'm gonna go for a 0-coast or a mother 32 (and maybe an SQ-1) for the moment and see if I need to build from there.