" I can't decide if I'm just lusting for cool oscillators because they're fun, or if I really need 4 oscillators in this system. I'm confused on how you would suggest going about this, especially with the Plaits and the BIA in the case, I feel like those are 2 sound sources that might be hard to complement... of course I could be wrong.... do you see it as simply playing the Plaits and an analog osc with the same sequence, going to the same filter and becoming 1 sound"
Yes, limit yourself to two oscillators to learn how to modulate them! I have Plaits and BIA in my small 6u system and what I do is feed them into my hex vca and modulate them with Quadrax and Kermit LFOs in random patterns for pure variety. Modulation and CV is key to modular. You can take one oscillator and split it up many ways to create a palette of tones. That is what I really enjoy doing. I modulate BIA so it has a percussion and bass sounds for a full track.