I’ve just skim read this thread (funny in places !) so my answer to the first question which I think was essentially can I use Hall effect sensors instead of proximity sensors for homing -

They require a magnet to get close to the target to trigger and so like all magnets in the workshop will grow metal hairs and become unreliable. I have one to play with on my new E-kart foot throttle. Great if the magnet and sensor can be sealed in a box but I think one part must ride on the gantry for CNC machines if they are the sole sensor so they can’t be protected.

However for the auxiliary use as discussed they can be enclosed on the end of the stepper shaft at the rear of the motor or off the ballscrew and be sealed off. (Like the twist throttle of an electric bike).