I designed and ordered the PCB.
This went fairly smooth, I made a few mistakes that I had to fix with some creative wiring, but I had two major problems:
I'm having trouble finding the right case. I bought one that almost fit, but left no space for giant 1/4" plugs.
After testing with several real guitars and microphones I found that voltage levels vary a lot from microphone to microphone, To fix this, I had to redesign the whole input stage to have automatic gain control.