An outboard Korg SQ-1 might be just the thing for keeping the MS-20 in check with the rest of your system.
SEEK or the Varigate 4+ are other nice sequencers to check out besides SHmkII. Also have you thought about any FX in eurorack or a mixer? Also why not get another VCO, noise source and a WAV player like TipTop One or Pico Drums to get some different flavor in there for small HP.