Yep, the Vector is HUGE...but then, it's clearly the "core" of the system, and even the build layout is set up to reflect this.
There's not much in the way of issues here. About the only thing I can suggest would be to lose the LINK2 and Links and use the space for a Happy Nerding 3xVCA, which would give you VCA control over the VCO mixing. Also, you could add VCA level control to the Doepfer A-138s by yanking the A-138n and replacing it with two 2hp VCAs, which would give you the requisite four VCAs as your mixer's "front end".
And I get it re: the quantizer...by having a second quantizer with definable scales, you can then feed it a clock from the sequencer AND modulation signals. By constraining the scales to match what the Vector's internal quantizers are set for, you can generate psuedorandom contrapuntal patterns from keying the extra quantizer via the Vector and feeding LFOs, envelopes, etc to the quantizer's CV input. A very sneaky and low-power method for complementing the Vector, to be sure!