Simple switches are VERY easy to hook up to a controller like this.
Input pins on the port have a weak pull-up. IE: they are 4.8v by default. If you tie the pin to ground, you just flipped the circuit.
(printer port ground, NOT power ground)
Simple as that.
NC(normally closed) switches are best for CNC since they will trigger if there is a wire break. *Nothing* worse than stomping on an Estop button whose hookup wire broke a week ago.