I'm looking into building a Eurorack setup around the Mother-32,
I don't know exactly what to add or what I really need,
I've looked into Eurorack modules a little bit, but I will obviously continue to do research

Well, that's a bit of a pickle because in order to make suggestions, one would need to know the problem or challenge to address, and you have not worded that at all. Do you feel limited by some aspects of the M32 and if so which ones ? Do you own any other gear ? Why do you want to go the Eurorack route instead of say, a couple of other semi-modular and desktop synths, are those cheaper devices incapable of doing something you like ? What sort of sounds do you hope to achieve ? "really unique and interesting sounds" is pretty much what everyone would say, nobody wants "boring and worn-out" sounds, but what does it mean for YOU ? Usually people like to include example tracks and even sometimes point to an instrument sound at a timestamp in a video.

  1. Should I add another Moog semi-modular synth? The Subharmonicon looks really cool.
  2. Should I remove anything that I have currently put into the system?
  3. Are there any essential types of utility modules that I'm missing here?
  4. Is anything in the current system not compatible with the other things going on? Its hard to know what works well with other things.
  5. The goal is to be able to create really unique and interesting sounds and to be able to use lots of different sources for modulation. What are the most flexible modules that I could add to this particular setup?
    I know that what I've provided is kinda only a skeleton of a full modular system, but I didn't want to bloat it up with modules that I didn't understand yet.

I agree with jb that planning to put the M32 in the Rackbrute long term would be a waste of money. Same goes for another semi-modular, why not add one if you want, but again, not in the rack if it already has its own.
As I said, I can't really start approaching the other questions (what is missing, utilities - you will need them but which ones, modulation) without you explaining what I refer to at the start, but VCA's, LFO's and mixing are bound to come into play regardless of goals and style, I think.

--- Voltage control all the things ---