I don't always like to make specific recommendations, but I'll make suggestions here. Anything I recommend here will be easily sold to acquire something else if you decide to try it and don't like it. Just remember to learn about something as much as possible before buying so you know what you're getting into. Also, please don't buy too many things at once - with a Mother 32 and what you already have, it should be no trouble to go one or two at a time and get comfortable with each module.
If I were you, I would get that Maths. Personally, I'd also be looking at something like the Buchla Tiptop 281t or the Doepfer 143-1 or 143-2. I love the Tiptop one because it's cheap, super functional, and can run a lot of stuff. It can do everything from envelopes to LFOs and even some freeform sequencing if you use it creatively. It just makes my setup come alive. It also gives you lots of individual control of attack and decay, as well as some fun gates and the chance for ratchets. But just look on this site and filter your search by Envelope Generators and Quad, then check out the most popular ones. If you don't mind a bit of fiddling and a screen, the Xaoc Zadar is a really interesting one that is pretty limitless in what you can make.
The Divkid OCHD and its expander are also useful. 8 LFOs in the original unit controlled by a single knob, so you get 8 different modulations but they all connect to each other. You can always use VCAs or attenuverters on individual outputs. The expander gives you more outputs based on the LFOs (the manual can explain them way better than I can here). It's great for creating patches that are unified, but not necessarily by typical musical means.
The Disting Mk4 or Disting EX are great modules for 2 reasons. They have tons of algorithms they can switch between to fill in holes in your system. In addition, you can teach yourself a lot about modular by learning all the functions available and how they can be used, helping you to figure out what you need more or less of (or more or less control over). They can be both great fun and good homework. Ornament and Crime, in various forms, is another great example of this - maybe even moreso because of its focus on modulation, sequencing, and CV tools.
Another thing I like that would fit your "unpredictable patching" logic is the WORNG Vector space. It's hard to describe, but you basically plug in 3 modulations and it gives you 17 different versions and variations on them. To me, this is a nice cheap (albeit big) way to get into the sort of Serge style of patches where you're not really thinking of the traditional musical components and instead just getting the function from the circuit and letting the musical results flow from that. Some of the best modules are the ones that defy simple description in musical terms, and you sort of just have to sniff these out by reading about them.
If you don't already have a way to get your guitar to Eurorack levels, that might be a good idea. Not only for processing the audio, but also using the guitar sound plugged into an envelope follower (like Maths) to control stuff on the synth. You have an amazing modulation and sound source that many of us can't have even if we throw thousands of dollars at the issue. You should use it. Plus Moog synths make great pedals. Imagine having a Moogerfooger 101 with a built-in 32 step sequencer. Turns out you do.
Lastly, I'd look into a matrix mixer that can take CV - there are lots of good options. I have one from BearModules. Honestly, Etsy is a good place to look for these. Low Gain Electronics makes some nice ones, too.
Filters are personal. Just look at a bunch and learn the different types. Don't cop out in terms of size for your filter, either. You want a decent, usable cutoff knob that you can access.