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Maths is very valuable for all kinds of different modulation. I've got one and have barely scratched the surface. I would recommend downloading the manual/patchbook and looking through it to decide if it is what you need. There's also a great video on YouTube by Loopop called "22 Reasons the #1 Eurorack Module is Maths." With that being said, it is a large module (20hp) which would take up most of the space in your case. As a beginner, I've also found it a little unintuitive and not immediately gratifying in my experience. You have to put in a little work into understanding what it is doing to get creative and get the most out of it. If you decide to expand to a large case, Maths would ultimately be very useful for you due to its functionality.
I just picked up a Pique from After Later Audio. It ships with the "Dead Man's Catch" firmware installed which adds a bunch of different modes to the original firmware. All sorts of different LFO, envelopes, drum sounds, and even a mini Turing Machine and sequencer. Again, take a look through the "Dead Man's Catch" manual (https://github.com/timchurches/Mutated-Mutables/releases/tag/DMC-v0.7-beta) to decide if it's right for you. In a small case, I would probably find a use for Pique and a small mult in every patch. It doesn't have a bunch of patch points to "modulate your modulation," but it does a lot right out of the box and could probably help you decide what you may want to invest in next.
Hope this helps!