Hi,
To begin with, you will need some modulation sources. BIA needs a lot of modulation to shine. You could replace Steppy (it only generates triggers) with a NE Mimetic digitalis type sequencer (triggers and CV), which fits very well with BIA
https://www.modulargrid.net/e/noise-engineering-mimetic-digitalis-black
Pam's also gives you many trigger/modulation options.
https://www.modulargrid.net/e/alm-busy-circuits-alm017-pamela-s-new-workout.
With the limited space you have, and given that the two voices are "complete" in themselves, perhaps you would not need a filter, but I would add some effects module (delay / reverb) and the leftover space some VCA, mixer for CV ....but I would definitely start with a bigger case.