Im doing something similar, but software only so I can remote control my daw. Logic has something natively built for that, but not most other daws and but most HUI options available are either only for iPad or a bit overly complicated. When you get to Software look for a capable MIDI HUI (Mackie control protocol) library. It’ll save you ages.

For hardware I’d assume you’d either Frankenstein a prototype out of old parts or 3D print something. Quick google search even turned this up

https://hackaday.com/2015/07/12/3d-printed-modular-keyboard/

https://www.instructables.com/3D-Printed-1-Octave-Piano/?amp...