The idea was to be able to play polyphonically and also have some slots leftover for random lfos etc. But I'm sure 1 expander would be good. If I drop one of those any suggestions for another 4hp module to fill the case?
I'm a big fan of Trent Reznor and his experimental scores so this will heavily be a sound design rack...however I want to be able to play live with my keystep pro. Bitbox for percussion, keystep pro sequencing that. Then I have many voices leftover in my rack.
-- echo7
For FH-2 polyphonic playing you could setup in the configuration tool:
Type: Poly, 2 Voices;
Per Voice Ouputs: CV, Gate or Trigger, Velocity(?) and Envelope(?). ( 4 x 4 )
Then you'd have a full 8 expander outputs for whatever—the filter and repeater, one of the Noise Engineering modules, bitbox?
You have two oscillators yes, so to play your rig polyphonically you'd have to patch both oscillators and mix them down to a single centred output so you can then bring them into your reverb, delay effects and make them stereo. Otherwise you'll have two voices, one in left side, one in right—probably not what you want. Of course you can record each voice separately and have as many layers as you want in your DAW. But you basically have two subtractive signal paths osc/bb>filter>fx and osc/bb>fx>filter, so this is not gonna be complicated.
The bitbox does multisample polyphony too with MIDI, so you have that option with your Keystep.
If you dropped an expander there is the Disting, I don't have it but it is VERY POPULAR—44128 racks.
https://www.modulargrid.net/e/expert-sleepers-disting-mk4
or since you're doing sound design you could look into the Happy Nerding FX—also well liked and popular, also something I don't have, haha. https://www.modulargrid.net/e/happy-nerding-fx-aid-black-gold
Ultimately it comes down to you. Personally I'd probably not devote so much hp in a small case to a reverb and two different delays... but your name is Echo so that's your thing. Do your thing.