I used the teardown instructions on ifixit to get the Mini apart. After getting in, I decided the strip out the main board, antennas and electronics and see what parts I had available.

ifixit teardown guide: https://www.ifixit.com/Teardown/Google+Nest+Mini+(2nd+generation)+Teardown/130974

It was at this stage I decided that I could make this a speaker, eventually deciding on putting in a Pi Zero W, where the original mini circuitry was.