Vcas are necessary because the gate and control levels of everything. Want to control vibrato over time? Use a VCA between your LFO and oscillator with an envelope generator opening and closing the VCA. This is where a modular shines over fixed architecture. Anything can modulate anything, and it's the dynamics and movement through vcas, cv switches, logic, etc that opens up everything. Effects are fun, oscillators are necessary, but to really get them moving, you need dynamic voltage, and that's achieved through vcas.
Take a look at your DPO. You might not know it but there's a bunch of vcas built in already. One to control fm between the oscs, one to control osc modulation to the timbre section, etc.
The uMod 2 is a great choice because you can use it as a VCA in addition to ring mod. Plus the lower section is amazing fir creative cv processing.
Unfortunately the mutagen has been discontinued a while ago, but the mutamix is its replacement and quite great. It's 18hp though, versus the 12hp of the mutagen. Still a good choice because of the 3 output buses. Not to mention its sequencing capabilities.
If you replaced the dub Jr. with a Disting (which has ping pong delays, tape delays, in addition to tons of other functions, of course) then you'd have space for the mutamix.