Thanks for the info on you background.
Well, your system here is pretty basic... which isn't a bad thing. There are a few things that would be helpful to you as you go along. Attenuators and attenuverters are good things. Not all your CV ins have attenuaters/verters built in. The Maths has four channels, channels 2 and 3 can be used as attenuverters. You may find yourself wanting dedicated units. The Befaco dual attenuverter is pretty tasty. It also includes an offset knob. This will give you a lot more control over your CV signals.
Eventually, you're going to want to tie this system into your DAW at least for sync and recording. So a MIDI-to-CV module would be useful as well as a mixer and Eurorack level to line level output. You can probably get away with not having either depending on your audio interface and its specifics (DC filtering, enough headroom to handle a HOT Eurorack signal).
A second VCO will probably be a good purchase as just one might sound a little thin for some applications. You'll also benefit from being able to sync two oscillators to get that "oscillator sync" sound and even do some audio rate modulation of things like filter cutoff etc.
There are a million directions to go in and everyone's journey is going to be a lot different. Don't worry too much about a module that is popular and everyone else seems to have. There are no presets in Eurorack and you'll find that a small nudge of a knob can often make a HUGE difference in what's coming out of the speakers. You can give ten guys the exact same set-up and get ten very unique sounding results. That's the beauty of Eurorack. But about the cost... lol...