Well, for AUX send-return stuff, start here: https://www.modulargrid.net/e/ladik-m-053-3-ch-aux-mixer This allows you to return three different stereo processors to a single stereo AUX return. As for the send part, I would suggest using buffered mults here to keep your send levels up and close to identical for all processors.
Now, as for transitional links, one potential solution would be to use a Tiptop ONE player with some prerecorded material (or suitable loops) so that you're "covered" while changing the rest of the patch. This also gives your live set a "ground point" to start with between each piece, so that if (or more likely, when) things DO fuck up horribly, you can at least return to a sonic point where you can regroup.
However, I have a few issues with the build as it stands now. First up, that DFAM doesn't belong in there. It might be convenient that way, but the truth is that you're wasting 60 hp in this cab on a device that already has power and a housing. That space is FAR better used for things that have NO power and NO housing. Secondly, the cost...one thing that puzzles me is, if there's so many modules in here, why are there so few sources? I only see two: the Verbos Harmonic Oscillator and the E-RM Polygogo. And much of the rest of the space depends on these large, spendy modules that might work better as smaller and less-expensive alternatives. Lastly, keep in mind that we're finally getting actual Buchla Eurorack modules starting around Xmas, and these are quite different critters from the Verbos modules in a number of cases. Take the difference between the Dual Envelope at 22 hp for $479 and the Tiptop Quad Function Generator 281t with 28 hp for a projected street of $210. I know what I would rather have...and not merely due to the huge price difference!