Hi Cedric,
Sure glad to help as always. The reason why I recommend a much larger rack from the get go is to not repeat the stupid mistakes that I made this year when I got started with my first modular system. I bought a Doepfer A100 Basic System 6U that was half full of Doepfer modules which are superb but quickly filled that up and then bought an empty Doepfer 6U case/power that was filled quickly as well. The fun modules tend to be quite pigs in HP size and want 20-30HP easily for a complex oscillator or large drum voice and that is why a larger case is best even if you only need less to start. You can fill in gaps with cheap blank HP slates and decorate those as you expand. Heck now with 2 full Doepfer 6U cases, I just bought a much larger empty case 14U MDLR so I won't keep running into this issue. You can always get a small skiff pod case if you want to do anything mobile.