also a guitar player here...
rack brute is ok - but wastes 5hp of your rack with it's rack wart... get a tiptop mantis isnstead - only a little bit more expensive - but no rack wart so over 40hp more rack space - it'll also mean you don't have to go for micro modules - you may still be able to pick up a real rings - much better ergonomics
for guitar input - take a look at the sonicsmith converter ev1 - ears only does amplification to modular level and envelope following - the ev1 adds a vco and the best pitch to cv converter available at the moment...
as a guitarist it's a good idea to be able to have some control with your feet (as you hands will be occupied with the guitar - expression pedals and on/off switches etc - addac are the people for that - or doepfer
if you already have the zoia, why would you want to duplicate it in the rack - especially as it takes up so much space - which is better used for other things - I'd swap the quad vca for a veils (should still be able to get one), 2hp smaller and better features imo
you may or may not need an output module, depending on what you are sending the signal to (most modern mixers and audio interfaces can cope with modular levels perfectly well - so unless you need balanced outputs the most you should need is some passive attenuators...
other than that filters and utilities (think plumbing - a rack without utilities is like a house without plumbing) would be what I would fill the rest of the space up with
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities