I don't know, man... 10 buffered mults? Two Pam's?
The folks that commented before are definitely pointing you in the right direction, especially for a case this size. Everyone is going to do this modular thing differently, for sure, but I can't imagine this is the best use of the limited space you are giving yourself. Are you planning on using the PNWs as your main sequencer, or do you have something external to sequence pitch more effectively?
I'm not a Maths disciple, but since you brought it up twice, it is excellent as Jim said for grasping and accessing the fundamentals of MODULAR synthesis. You may have years of experience with synthesis, but trying to cram all of the functionality of a fixed architecture synth into the small euro case you have selected is very difficult (impossible?), hence the Maths love. Need a mixer? Need a subharmonic generator? Need to attenuvert four different envelopes? Need a basic logic function? Need to create a weird shifting bouncing ball envelope? Maths... It doesn't have to be a complex signal chain. It just gives you all of the stuff you are ultimately going to need more than 10 buffered mults.
The PanMix is euro level. You probably won't need an external output module.
Have fun and good luck!