New 3U system; Next steps?

I just bought a 104hp 3U skiff:
ModularGrid Rack

My budget was limited so I stuck with a pared down PGH System 10 and Clouds. I also have a QuNexus for CV/gate and other control. Mostly I am aiming at ambient, west-coast influenced music (although not Morton Subotnick plings and atonal percussion, more like FM/waveshaping and complex envelopes). I am thinking of adding on something like a Quadra or Maths plus perhaps another VCA like an Optomix or uVCA. Any suggestions on good next steps? I don't want to expand beyond my current rack for a while, so space is an issue.

Thanks~!