(Optional)Rotary Encoder, most marked for Arduino will work, none with the PCB included
Detailed part notes:
MX switches which support SMD LEDs will give the best backlighting effect. Almost all Kailh switches have a cutout for the LED. All Kailh Choc low profile switches also have a cutout for the LED. Kailh BOX/Choc switches will not be able to have their tops opened after soldering. Cherry and Gateron have a lineup of RGB switches. Any switch with a transparent bottom housing will work great.
The PCB supports Holtite 8P2/8P2 sockets for the MX holes.. The Mill-Max sockets that are popular may not work.
For tenting you can get two pairs of the standard CNC feet that most 60% cases come with (found here or here) These will give you a ~5deg tilt.