Hmm...yeah, the Mutamix won't work here in the way you think. Plus, a system like this is VERY underserved by only a single VCA. You don't need the buffered mults, either, since you don't have enough CV destinations to cause voltage sag issues that would affect tuning and scaling. Also, farkas is VERY correct here about the layout/signal flow issues here; this will turn out to be a very unintuitive instrument to work with.
This is another example of "sexy module syndrome", really. You have nice things...but their purpose here isn't clear, nor do you have all of the "boring" utilities, such as attenuverters, mixers, etc that make this sort of thing function properly. You could probably rip half of this out and still get the basic, overall result you're aiming for, in the end. As for "beginner modular"...go look at perhaps the best example of that, the ARP 2600. These have been used for literally DECADES as teaching instruments, and probably the new ones still would be had Korg not lost its damn mind with their "limited reissue" BS. Now, I'm not saying to replicate the 2600...but pay attention to what it has, how it's laid out, and how you might update that to arrive at a good beginner result for yourself.