Yep...the big thrust of the West Coast and related designs is that they're more "texture" instruments. To get something "giggable" in a band sense, you'll probably want to stay in a lane that goes more in the subtractive area...straight-up VCO-VCF-VCA + modulators. Not that textural programming doesn't have a place in that sort of thing; David Bowie's "Heroes" is a great example of where washes of non-melody/non-harmony can work in a more "conventional" situation.
VCOs...really, you want two per voice. I know that you can get away with a single VCO, and many synths do just that. However, to get a really BIG sound, you can't beat having two VCOs, with one ever-so-slightly detuned.
Keystep: got. So the patchable in question should optimally have a MIDI-CV capability in addition to the normal CV/gate patching methods. This simplifies control, keeps the patchcord jungle a tad more manageable.
Filter: decent LP VCF or similar. Need EGs, need LFOs, but nothing too out of control.
So basically, something like an ARP 2600-ish architecture, minus a VCO, but with duophony. The device that immediately comes to mind is...........drumroll, please.......................the Plankton ANTS!. Costs the same as a Mother 32...but it's definitely NOT a Mother 32. Yep, you get duophony via MIDI, 4 VCOs, a multimode VCF, dual EGs, dual LFOs, dual VCAs, noise, an AND gate, sample and hold, 3-in mixer...in short, all of the basics and a little bit more, plus prepatching like the better patchables that you can defeat just by busting out the patchcords. And it's a little-bitty thing: 222 x 132 x 45mm; it and the Keystep would fit in a smallish gigbag. And it most definitely expands via the Eurorack world, for later on. The sole thing of note it's missing are multiples...but on a Eurorack system this small, you'd be using inline mults or stackcables anyway. Pop over to https://www.planktonelectronics.com/ants/ to have a closer look.