0.2mm layer height with 36% infill has sufficed for me. No supports necessary. I have had success with both PLA and PETG. Be very careful when removing the keys from the print surface - the connections between the keys are thin, as they are meant to be flexible. PETG is nice for this purpose.
After inserting the keys through the back of the faceplate, it is ready to be installed. This faceplate replaces the bezel that comes with PocketCHIP, so remove the bezel. Then, taking care so that the keys do not fall out of the faceplate, snap into place. I find it is easiest to start with the two clips at the very top and work down. Some satisfying clicks later, you are good to go!
Removal is simple. Like the installation, I find it easiest to start with the clips at the very top. Carefully pop the clips off, and there you go!