1_ A Guitar into Beads is a fun idea. Beads has 'attenurandomizers' for randomizing the most creative aspects of the module so you can just sit back, jam, and get lost—I've played a guitar into Beads for hours in the dark.
2_ For Drums, have you seen the Percussion Interface from 4ms?
I love envelope followers! I think they are the most special, magical modules to have. Everyone, but kids especially, light up when they scrape or hit a surface or pluck a spring and hear some grand elaborate sound come out. It feels as though the sounds were generated by the surface touch 1:1. That's my favourite parlour trick.
3_ You're leaning heavy on the 'random' generative modules but as you're an acoustic musician also, I can't imagine you'd be amused by random for very long—like watching television with randomized channel changing—at some point the guitarist or drummer in you will kick in and you'll want the randomizing entertainment and the novelty to stop so you can develop a groove, or refine an idea to an expressive personal musical level. The "random abrupt percussive esque stuff" you like might not actually be random so much as unexpected, and that is the listeners perspective. Once in control of the modules, random, true randomness like chaotic arbitrariness can be either boring or anxiety inducing—you'll find yourself always twiddling knobs for a more 'refined', 'character', 'musical' sound.
4_ The good thing about the Intellijel 62 is that it is super popular. Put it in your search engine and image search all the other people with your exact case asking for advice and showing their setup. (Especially from r/modular and the Intellijel forum)
5_ 62HP is a great start. You could always buy a bigger case later and use the 62 for more portable duties. Modules like the Tetrapad and Planar are great to have as lap or close-at-hand controllers in a 62. This setup is a good explanation of what I mean when I say what sounds like random from the audiences perspective can actually be tightly controlled, hands-on performance modulation: (note: at 0:56 he set it to randomize only to quickly abandon it for the more controlled sound with the joystick and the sliders—he literally couldn't listen to more than 2 seconds of randomness before he turned it off. That's worth noting.)
6_ You can still buy C4RBN, just don't prolong buying it for very long. If you can't get a C4RBN there is the µVCF at 6HP and then Wasp, Ikarie, Ripples, etc at 8HP. A filter is one module that you will want to play hands-on. So that's where size is 'the bigger, the better' —Perhaps rethink having a Maths eat up 1/3 of your available rack space. You won't find many 62 cases with such a big utility module. (consider the Make Noise Function or Instruo Cnoc). But there's always more room in more racks. : )