I've not seen this mentioned but sometimes it's hard to find specific info here. I thinking about using one limit switch per axis, so take the Z axis for example, you mount a switch at the mid travel point on the Z 'fixed' backplate, then you position 2 strikers near each end of the Z 'moving' plate, these would have slotted brackets to allow adjustment. Now when the Z axis reaches either end of it's travel one of the strikers will activate the limit switch. Obviously same goes for X and Y and the switch could be mounted on the moving part instead if that was more suitable.
Any opinions about this ?