You're trying to do too much in too small a build. I would suggest losing the drum functionality altogether and going with a drum machine off the shelf, as it'll cost less in the long run, plus you'll get more out of one of those than just the snare and kick that's already there in this build.
Secondly, without modulation sources and VCAs, this'll sound as dull as dishwater. VCAs let you control amplitudes for both control and audio signals, and modulation sources can be used with them (envelopes, especially) to better articulate the notes, in addition to the "all-over" purpose of adding some animation to the patches.
Third, single skiffs like this aren't necessarily the best place to start. These are better suited for "mission-specific" builds, such as putting together a modulation "sidecar", extra sequencing, etc. You CAN get a whole synth into one, sure...but it's not all that simple, plus you have to make sure to NOT use big modules so that you can arrive at a playable device that provides all the functionality while not being so cramped that you can't use the instrument properly. A much better place to start would be Tiptop's Mantis case...hefty power, light weight, and not expensive at $350 or less depending on where you are. With 2 x 104 hp, you have plenty of room for modules such as the Nerdseq and Dual FX AND you can get everything else in there that should be in there.