@Paco_Raap I’m not sure I’ve internalized all you’ve done, but my gut is that you should be able to setup a proper homing situation with your mill. I run Marlin on my mill (without endstops), but know I could if I wanted to. I think maybe one of your settings is either inverted improperly or missing an opposing setting. You should be able to use Z max + endstop as the Z at its highest point. I think the gcode to do that (and set Z = 0) would be:
G28
G92 Z0