I decided to build my own FFBoard-based wheel a while back, alongside a friend.
We ended up using different motors, wheels and he even opted for a quick-release.

We bought cheap 21mm slip rings for signaling, which have a place in the center of these adapters.
I'd recommend you print one with low infill to use as a drill guide, as you'll need M5 screws to fit the adapter to the motor/rim.

Before printing, check to see if the pattern matches.
My prints were in 0.2mm layer height with a 0.4mm nozzle. PLA works fine, as does PET-G.

Models are upside down for some reason - print with the rim pattern facing up.

I also attached the FreeCAD file if anyone wants to adapt this to their needs.