My take on the dual ADSR issue would be to check into Doepfer's basic but space-economic Dual ADSR...fits into 8 hp, and you lose the looping switches, but you don't usually loop ADSRs anyway. I'm also not jazzed by using a Rosie as the final mixer...it's more akin to a DJ mixer's output stage, and while that might work in some cases, this probably isn't going to be one of them. Lastly, don't fall into the "drums in a small build" trap here...these sorts of cabs do NOT have the space for a complement of drum modules AND the rest of the stuff. Use a proper drum machine instead, and lock it up to the DAW's MIDI clock.
Definitely need a VCF, though...but that sort of depends on what you're trying to do musically. Some are fine for all purposes, but others are more specific to certain styles. Also, make sure to keep the layout in some sort of order that makes signal routing sense, such as keeping the audio modules together and in a flow that tends to go VCO-VCF-VCA for ease of use.