I like where you’re going with this—especially with the Vector.
I think the Recombination Engine takes a really interesting approach—the waveforms on the scope are gorgeous—but in the end I think I'd got with an Instruō Cs-L to expand the palette of synthesis approaches. IMHO the Cs-L is even more versatile with its two oscillators with different cores, two different PWM circuits, two different wavefolders, and a VCA that can all be used independently, but they’re configured in just the right way to multiply their functionality many times over with hard and soft sync, ring mod, FM, etc. I expect it'd also make the FLD6 redundant.
With the 6hp I'd save I could add a Select 2 from Joranalogue if I wanted some audio rate switching like the Recombination Engine's "scissor" function. I could also add a different third oscillator like an MCO from ALM, or maybe a characterful filter like the Cinnamon from Bastl.
Also, if I had the Vector sequencer at the center of a rack this size, I’d definitely think hard about adding the Jack Expander to get the most out of it. I might also slide the Vector to the left side of the case to increase access to the big knob on the left side of the module that does so much of the work.
Lastly, for me the mixer/VCA situation seems a little disjunct with the Doepfer mixers and Quad VCA. Mixers with built-in VCAs can work double duty. Maybe look at good old Veils, the Joranalogue Mix 3, or ALT from Nano. But for a performance rack I'd start with the Xaoc Praga. It's a little larger but deceptively capable. It's actually got 8 ins (4 channels + 4 returns), 8 outs (2 main, 2 sends, and one on each channel), 4 VCAs, 4 stereo panners under CV control, switchable curves, and performable mutes.