You're not going to be able to use that external mixer for CVs and mod signals, though...and you NEED that functionality here.
This build has lots of sources, to be sure. BUUUUUUUUT...
...as usual, there's lots of utility stuff that should be here...which isn't. You got the "sexy" part...and ran a bit too far with it, seems like. Jim's advice is very good. I would also suggest removing the drum modules; fact is, you can probably get more cohesive results with a present-day drum machine than by trying to work with this in what's actually a rather sonically-crowded and not all that big build. You would be in a far better position and have a much better build if you did this, then reallocated the space as Jim (and I!) suggest.