I note the absence of VCAs here...even with designs that replicate the old-school East Coast architecture, you're gonna want a few of those. My suggestion would be to yank the Chatterbox and panners, then put in a stereo VCA mixer that has the panning functions on CV, and use whatever space is left for a couple of linear, DC-coupled VCAs for CV amplitudes. Also, you might consider a bit of a nod to the West Coast (and adding some killer functionality) by pulling the A-145 and 146 and replacing them with Doepfer's A-171-2s. They're basically a rework of the Serge VCS via Ken Stone's redesign. I'm supposing you're planning on using in-line mults. Lastly, have a look at Expert Sleepers' FH-2 as a substitute for the Doepfer A-190-3...much more flexible, and expandable to boot.
And as for the second cab...what? You're considering stopping at TWO?