OK...one more shot here. I blew your budgeting all to hell, but I wanted to suggest what an instrument of the sort you were discussing could actually be. Here it is...
Now, you'll notice first off that the case is different. Instead of a Doepfer 84 single row, I went with an Intellijel 4U/104. This opened up a bit more space, plus added the Intellijel tile row for some extra functions, and it's fully-powered with Intellijel's excellent integrated supply/power bus. From left to right up there, you'll see your main clock, noise sources, a slew limiter, sample and hold (in the first tile alone, too!), a 4 x 64-step trigger sequencer for your drums as well as clock modulation/tinkering, a Quadratt which is your CV linear mixer/mult/inverter, then the line in/out which uses the Intellijel case's I/O jacks, already built in.
Bottom row, left to right again: the Permutations is a generative randomness sequencer based on the popular Turing Machine, sort of a 2nd-gen version of that. This provides loads of random and psuedorandom (at varying levels) CV possibilities. Next to this is a Toppobrillo Quantimator, a quantizer with scaling/tuning/chordal control via CVs, plus three outputs which can also be fed via an analog shift register, a sample-and-hold-type device which feeds CVs forward by a step on each clock pulse. These three outs are also your chord outputs, as well.
And with three outputs, you need three VCOs. I opted for the Noise Reap uBermuda here...very cost effective, plus they have a very crazed self-regen control that can drive the VCO waveforms into some really nasty shapes for lots of distortive harmonic fun. Audio mixer is next to these to sum your VCOs down.
The Delptronics LDB2 setup is next. This is a pair of modules (voices and CV expander) that offers analog sounds in the typical Roland 606/808-type family, with CV control over numerous parameters. Next is a pair of linear VCAs, to be used with CV/mod signals to control their levels. And for modulation, that's now fairly comprehensive: a Takaab triple LFO, Takaab CVable A/R envelope, and dual Doepfer ADSRs. Note the location, also...the Quadratt is directly above so that you can easily route your mod sources into it to combine them.
More Noise Reap...state-variable VCF with three frequency CVs, plus CVable resonance. Another audio mixer allows you to sum the outputs from this along with the mix out from the LDB2, if you choose. Right next to this is a switchable linear/exponential VCA with built-in AR envelope for your outgoing audio level control prior to the effects: 106 Chorus (again) which can stereoize your mono audio to feed direct to the uClouds SE for more processing, with the audio outputs directly above for convenience.
Yes, I know it's about $1500 more. However, this is the sort of thing you're actually pointing towards with the ideas you'd mentioned, so I thought you might like to see a reference of what this might entail. Oh, and as for the passive mults...there are none. In this tight a space, it's best to use inline mult widgets so you can maximize your active functions. And while there's buffering on the Quadratt output(s), there's no buffered mult because you won't be connecting CVs across so many modules that would cause voltage sag.