If you're going to connect some switches on your MuIn USB (using your firmware), you can consider using PORTB since it has integrated pull-up resistors: one pin of the switch will be connected to GND and other pin on PORTB Input. You'll detect the button pressed with some instructions like those:
if (!LATBbits.LATBx) // x=0...7
// instructions to execute if button pressed
// instructions to execute if button not pressed
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