Good Morning,
I am planning on running power from the ATXRaspi to my Pi3 via GPIO pins. What gauge wire would you recommend for the power? I am running 22AWG for the LED and Switch, but wasn't sure if that was low enough for the 5v line.
22AWG should be fine. The weak points are usually the connectors not the wire itself.
Ok thanks. I'll probably use 20AWG since I have some laying around.
Also, what current rating should the switch be? I have one good for 500mA momentary, but I see the one you're using is rated for 3A.
The switch rating does not matter since it does not pass current through. It's only used by the ATXRaspi. Any tactile momentary switch will work.