Ahhh I get it now!! So the trigger height is just a reference position and the z0 command will be given to the printer when printing by the slicers g code?
Mostly correct but actually the first Z move will be to the Z position that corresponds to your first layer height is - i.e something like G1 Z0.3.
The M574 command overrides M558 now. So use Z0 in M574 to use a Z probe for Z homing.
Assuming your want to do bed probing with the nozzle and bed at printing temperatures, then it's best to calibrate the Z probe trigger height at operating temperature too.
I've never built a CoreXY printer. In theory 0.9deg motors would give you more precise positioning, but in practice I doubt you will be able to detect any difference.
