If you are really new to this and as you say "go through the phase of just plugging things in and see what happens" I'd suggest you may benefit from an oscilloscope.
It's one of those modules that you may think unnecessary, but time and again I've seen even seasoned modular fanatics benefit from being able to visually see what their CV is doing.
Wrapping your head around the actual working functions of things will help you better approach your build as well, IMO, YMMV.
You could get something small, like the Intellijel oscilloscope, or the Mordax DATA if you want to have the absolute best, and could always sell it down the line when you feel more confident in anticipating what each module will do when you patch it.
As to MATHS, it's giant, but it does afford a lot of opportunities, as long as you are willing to sit with it. Just off the top of my head, combined with DFAM, you would be able to achieve a great many rhythmic modulations with just that module, paired with Pam's you will be surprised at the variety, and as someone mentioned, paired with another function generator as well you'd have a never-ending way of creating modulating patterns and timbres.
Get more VCA's than you think you need as well.