Over the course of beta testing the new Rene v2, I found it paired really well with the 0-Coast. Using one sequence for quantized pitch+gate, and the other sequences for triggering the Slope generator and un-quantized CV for modulation of other parameters. Tempi was also useful in addition, since it has integration with R2 and provided a way to clock the sequences and MOD inputs separately (as opposed to mult’ing the 0-Coast clock to the X/Y clock inputs).
I guess if you’re mainly sequencing via MIDI, I’d suggest something like Maths. The combo of voltage mixing/or/inversion, plus function generators really augments what’s already there on the 0-Coast. The 0-Coast actually has quite a bit of modulation outputs, but the onboard mixer is only two inputs. For single module, the multi-purposefulness of Maths goes a long away too. Clock division, Gate delay/width modulation, burst generation, slew/portamento, etc.