Yerwelcome! For me, this is working from experience; having been working with different types of electronic instrumentation for about 40 years now, ranging from cobbled-together breadboards and bits up to drool-worthy modular systems, I'm just real used to how these things should work. But there's a few things I routinely do:
1) Cluster the functions. I always try to get the different module functions in the same general areas. That way, you know where the thing you're looking for in general is going to be, and you can move around and patch very rapidly once the layout's learned...which, again, this clustering makes easy.
2) Follow a model that works. As a rule, my overall layouts follow a distinct order of function placement, which is actually based on a still-coveted classic that I've used off and on since 1980: the ARP 2600. When you get a chance, have a look at one, then compare this build to that. The ARP 2600 is such a desirable synth because not only does it sound great, it has an easily-navigable layout. You know where the VCOs are (upper left), the filter is (dead-center), and the VCA and reverb is (right end), with various modifying things on the lower tier of submodules. I recall a quote in Mark Vail's 'Vintage Synthesizers' book: "It's the only synth I can play when I'm drunk."...and there's very good reasons for that! Also, I find it a bit telling that two companies that built huge modular systems (namely, Moog and ARP) first then wound up going with much the same layout in their first portables (Minimoog and 2600, respectively): VCO->VCF->VCA, left to right, and control placed convenient to all of these.
3) Build to scale. These days, it's possible to get teensy modules with massive functions, and they're great when you're building in a tight space. On the other hand, if you're doing a big studio rig, go big with the modules. But make sure your form factors always fit the cab they're being chosen for. You want as much function as you can jam into the space you've specced out.
It also helps, probably, that ambient is what I've concentrated on musically in one way or another since the early 1980s. So I have a good idea of what'll function properly for that, and can choose accordingly.
As for the mixers in the tile row: yep, you got it. The Mix-A is DC-coupled, and a linear DC-coupled VCA is next to it. But the Mix-B is AC-coupled, and needed an exponential, AC-coupled VCA for its audio-only path. But that being said, you can easily use the two different VCAs as percussive amplitude control for differently-weighted noise types off of that Zlob module, with the linear one giving you a softer transient response and the exponential being perfect for hard, fast 'snaps'. And then, you just play the FSR's like teensy-weensy bongos!