Nice noisemakers in there...too bad there's not really a way to get them to really cut loose.
As noted above, start with a MUCH larger cab than you know you want. In other words, get stoopid! You may, in fact, find that the case wasn't as small as you'd thought! Starting larger also lets you lay out ideas such as module subsystems...you can discover groups of modules that work very synergistically that way, and once you've found something that works as a "system core" along those lines, THEN you'll know what case size to shoot for.
Also...and this is IMPORTANT...don't fill your build out with "sexy modules" while doing this exploration. Utility modules might not look all that jazzy, but they're 100% KEY to making a modular do what you'd expect out of it. F'rinstance, let's put in something utterly ridiculously expensive...a Cwejman RES-4 quad resonant filter. Wow! $800 of filter! Can I input just a little bit of LFO on one band's CV? Welllllll...do you have the cheapo external attenuator for that? Coz the Cwejman's not got ANY input attenuators.
That's one example. I could think of enough, though, that I would risk a brain aneurysm. If you leave those elements out, you ain't got crap...except for a very spendy box with some twiddly electronic noisemakers.
Since you also have VCV Rack, I'd suggest doing a little MG exploration with it. How? Simple...put up two windows. Work on your MG build in one...but in the other, put up VCV and "play along" as you build by building up...as close as you can...what you're assembling in the MG window. No, there's not a 1:1 equivalency there, but you'll have a really good handle on how, what, and where utilities work in the context of a patch, and this can help a lot when finally working out how much of a hole you want to burn in the Magic Plastic.