A few general points:
1) Think of ergonomics and playablity. If it's not easy and fun to play, you won't end up using it. Good on 2hp for doing an amazing job filling a niche, literally, but you really need to think about the playability of lots of little knobs next to each other. Are you really going to be able to comfortably tweak a parameter without knocking a different knob by accident? You should be thinking about spacing and tweakability as you go, so the system doesn't end up being a pain to play.
2) VCAs. I think a cascading VCA has more potential than 4 independent VCAs. Hard to beat 8 VCAs in that footprint, but you're missing out on some interesting functionality.
3) Drums in rack. People often caution against going drums in rack cuz it's not the most price or space effective way of getting drums, but hey, you do you. Personally, I think they're fun. However, you might want to consider a cv controllable sampler like vpme.de's quad drums, a bitbox, or the assimil8or (which is an absolute dream, by the way). They aren't analog, but they will give you a tremendous amount of flexibity in a relatively small footprint. They tend to be pricey, however.
4) Too much hp spent on sound sources. Sorry, but in a rack this size, you should be limiting your oscillators and sound sources so you can spare room for the other types of modules (like utlities) that really help set modular apart.
5) Utilities! You have attenuators and VCAs and mixers, but there are some interesting other options that can play nicely with rhythm based music. Logic modules, comparators, clock modulators, routers/switches, and sample and holds are just a few types of modules that can really help add intricacy and complexity to your sequences and rhythms and give you a ton of flexibilty. Take some time looking through the different utilities listed on here, or watch some videos about the types listed above. You'll probably be getting ideas popping off in no time.
6) Computer connections. Depending on what you're aiming for you might be interested in connecting your system directly to your computer. That way you can record directly to your DAW or, more interestingly, use your rack in conjunction with software modular programs like VCV rack or voltage modular (I think there are a few others now, too). Something like Expert Sleeper's ES-8 or ES-9 (both come in black) do this magically.
Anyways, best of luck!