Aluminium Profile Type Router - Initial questions

[Kitwn]

Other way round! NC will normally be at ground voltage (Normally Closed to ground) until triggered. "Normal' means you have NOT driven the machine to it's limit and it is continuing to cut material as intended. This gives you protection against broken wires as an open wire shows up as a high voltage if your controller has it's own pull-up resistors and the machine stops. Failure of a NO connection only shows up when the limit switch fails to make the ground connection required and your gantry crashes through both the limit switch and the end wall of your shed.

My personal preference is for one switch per input as you are planning. NC is best as explained above but NO is more commonly available, presumably because of the ease of parallel connection.