+1 for everything Jim says (as always)
You should expect your system to evolve as your needs change. The best advice I recieved is to start with just a few modules and learn how they fit into your workflow, then start adding modules that will expand and support your workflow
Mutable Instruments made some of the most innovative modules that have a bunch of different ways of patching. Stages for example can be envelopes/LFOs/StepSequencer or an oscillator. Great choice to go with MI as a brand
If you'll be working with found sounds a sampler might be a great addition to this system. ALM Squid or BitBox would be awesome.
Here's where I would start based on your description:
Keystep - Midi-CV
Clock - Pam's (for clocks and slow evolving LFO/Random)
Sound Source - Plaits
Filter - to taste (Cinnamon, Ikari, Wasp, lot's of great choices)
Sampler - BitBox Micro (also has Midi in)
External - Somethign to make connecting Mic or 1/4 instrument easy
Modulation - Stages/Clone for Envelopes and modulation
VCA - Veils/Clone
FX - to taste (Morphagene and Memeophone are very good, but there are TONS of amazing FX)
Audio Mixer - Something that interfaces with your other equipment well
This would be a fine starter system with lots of flexibility. Then I'd start adding things like a Marbles clone and other things that are in your original system