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.-- ferranadsr
I agree with all of this. You will want and need a bigger case before you know it. To get the most out of any module, you will find the need for supporting modules. Supporting modules take up space. Imagine all of the functions in a fixed architecture synth or groovebox and then realize that you will need a lot of those functions, sometimes multiple copies of each function. Bigger case than you think you need is pretty much rule #1 in modular land.
Tweaking by hand is fun, but you only have two hands. BIA will require about six hands to get interesting grooves happening. I used the Voltage Block to get cool stuff happening when I had BIA. That's 8 lanes of sequenced modulation in 20hp, not to mention a gate source...
How will you be mixing? Do you want to automate volume and panning? Mixers, VCAs, and more modulation sources can help with this.
Unfortunately, minimal systems usually offer minimal results. The modular world will quickly eat up a lot of space and your bank account, so make sure you understand each part of what you're getting into. What is it that a tiny incomplete eurorack is offering that a groovebox with sequencer or fixed architecture synth doesn't offer?
Have fun and good luck!
*Edit - Just saw that Jim posted at the same time I did. I agree with all of Jim's thoughts regarding small racks.