Very cool lucianon ! I like the idea of putting the R-Pi inside and making a rompler.
Not for you but for anyone else reading this thread and thinking about making their own custom minisynth similar to what you are doing. There is a new 8 voice virtual analog small sized Eurorack module just announced at Superbooth 21 that sounds retro-ly awesome. As a part of that Eurorack module are compact controls for those sounds. It’s called the Poly-Cinematic from Knobula.
Here are link1 and link2 from the Superbooth thread. You can listen to it through those links. Beside the range of polyphonic “analog” voices it has a reverb built in. Perhaps then add a small MIDI arpeggiator, and/or LFO modulator to that.
I was thinking of this with a Waldorf KB37, but as that has been discontinued, and getting more expensive and difficult to find, as well as being more clunky in size. The approach you’re taking lucianon looks a much better option.