project update:
I've chosen the layout
six layers:
1: buttons, rotary encoders, GPIO expander n stuff
2: a big GND plane
3: not yet defined
4: power plane: i drew three rectangles for analog 3v3 and +-5V
5: GND and AGND planes, separated by ~5mm and connected at some point
6: esp32, connectors and audio stuff

i've tried using freeroute for routing some stuff. it gets kinda stuck at 30~50 unrouted nets which i'll have to route manually
it placed many vias.. i think i'll change them either into buried vias or microvias
the unconnected things are pretty hard to connect.. i ain't good at puzzles... damn
what do you think?

soon i'll publish every change made so far on the repo