First up, move the I/O jack pair modules to the ends of the 1U row and co-locate their functional modules there. This gets these cables out of the way of the patchpanel. Then dump the buffered mult, since you've really not got anything here that requires it; use some inline mults or stackcables instead to save space, and this would open up a bit more 1U space for something like Intellijel's reverb tile.
Reconsider your module ordering here, keeping your SV-1 in mind. Try and lay out the 3U modules in a similar manner to the SV-1, since this will make crosspatching the two systems a bit more intuitive. In other words: Steppy is left, then Plaits, Filter8. Above this (or close to it), relocate the clock/S&H/slew tile, since all of those are needed at left. After this, place modulation: Batumi, Function, Stages. The Mutamix should be at far right.
I'm presuming your MIDI interfacing is via the SV-1, so stacking that close by the Steppy, Plaits, clock, etc will be helpful.
Now for the bad news: you have no VCAs here save for the one (semi-dedicated) on the SV-1. Part of this is due to the mixer you've chosen; the Mutamix can automate mutes...but NOT levels since it has no CVs. You can add a Linix, since the Mutamix is designed to connect to that via a backplane connection. I wouldn't do that, though, since now we're talking about a 34 hp module pair that costs over $600. A much better choice would be a Toppobrillo Stereomix2...which then allows you voltage control over levels on each channel, panning on each, AUX send on each, a CUE send, AUX send/return for effects, etc...AND it costs $479 and fits in 24 hp. This then takes care of your audio VCAs, plus stereolocation, bringing FX in and out...but you also need a couple of VCAs for CVs and modulation signals so that you can control their amplitude as well. So, back to Intellijel and their uVCA2...a pair of summable DC-coupled VCAs with adjustable response. That should do the trick in only 6 hp.
Now...consider adding a waveshaper, perhaps. Tiptop's Fold Processor will add quite a bit of timbral variation, particularly if you route the Plaits through the SV-1's mixer to combine it with its VCOs, and then into the Fold before filtering. The Fold also gives you a suboctave generator...great for creating very destructive bass!
If you were to lose anything from the 3U modules here, it probably should be the Make Noise Function. For one thing, you have a dedicated EG in the SV-1. Secondly, there are smaller two-stage EGs out there, and you can probably jam that same sort of function into a smaller space with something like an ALM Pip Slope (4 hp), Erica PICO EG (3 hp), or a 2hp EG (2 hp...obviously!). Done right, you can cram all of the additional modules above into this 4U cab and it should just fit!
