caps... if your starting from scratch (no vintage parts), you'll have to decide if you want to go with SP or matias or even tai-hao (they have alps caps too). this will dictate what stabilizers you will need. unless you're really against vintage, i'd suggest getting one of the classics as a starting point. would provide you with a full set of usually decent/good caps, stabilizers for those caps, and a set of switches (even if they are not your preferred switch tactile/clicky/linear)
- tai-hao caps are thin ABS double shot
- apple alps caps are thicker dye subbed PBT (but some have different sized keys than a standard 104 layout, and some are rotated 90deg. ...AEK II F-row, etc.)
controller... just depends on the layout you want (how many rows + columns), how many I/O pins on the controller and how creative you want to get with the key matrix.
- do some digging on the feather ble, i believe there has been some limited success, but BLE is still very "new" in the DIY realm.