Hi Rickolls,
You got yourself some fantastic modules there planned (or did you bought them already?). It's just that I am missing a bit the "standard stuff". How about an extra LFO for example? How are you going to output your audio? Did you planned any audio output module (and perhaps an input too)? I see you got a mixer so that's good but I am missing an audio output module.
Since you mentioned it already yourself that you are not really have a purpose for that MIDI breakout module I would get rid of it, saves you 4 HP space. Today I just received the Erica Synths Black VC EG module, fantastic ADSR module, I love it. I bought it together with the extension module, up to you of course but I can recommend that module too. It provides you with single outputs for the ADSR (i.e. for each an output: Attack, Decay, Sustain, Release). The only stupid thing of that extension module is that's 5 HP...
So how about keeping the lower multiple but get rid of the upper multiple? For your relatively small layout perhaps one multiple should be enough? If you would get rid of one of those multiples, you get another 4 HP space free, then you could (if you want that) add that extension module and you still have 3 HP left. Erica Synths offers many different Pico modules (they are all 3 HP wide) so you can use that 3 HP space in the future for a Pico module (just as an example). If you still want a second multiple, in the Pico line there is a multiple (called Multi) available.
I would keep any way some space reserved if I would be you since you want to restrict yourself to just that 6U space. Keep another 8 or 10 HP in the lower row free for future use as well, it might come in handy. I wouldn't plan it totally full straight from the beginning that leaves you with no flexibility for the near future.
At the end all up to you of course :-) Good luck with the planning and kind regards,
Garfield Modular.
For review reports of Eurorack modules, please refer to https://garfieldmodular.net/ for PDF formatted downloads