Alright, so maybe the mixer and fx modules can go (for now). If you're really planning to only connect a keyboard, the FH-2 is overkill. Also, if you're planning on creating structured tracks a full eurorack sequencer does make sense. That said, I still think the Usta is just too large for a case this size. Anyway, I thought this posed a fun challenge and I've had another go:
Replaced the FH-2 with a simpler (and smaller) Intellijel uMidi (your keyboard does have Din Midi Out, right?). The MI Blinds got replaced by the smaller Vermona QuadroPol. I never agreed that everyone needs Maths, so that got divided by 2.5 to Function (bad pun, sorry!). Since you're using a keyboard you might actually want to have a full ADSR. The Xaoc Zadar can be used (almost) like a full ADSR, but also for all sorts of interesting wave shapes, both triggered or looped (all that x4). The WMD TimeWarp can act as dual slew, EG and envelope follower. All that should give you a bunch of cv sources + manipulation + mixing capabilities. Both the BIA + the EnOsc can use plenty of those. Also there now is a selection of three filters. Whether these work for you is a matter of taste.