This is like a health and safety thread on a model engineering site! ;-)

Commercial CNC machines rely on the spindle motor drive, with a suitable signal from the controller, to prevent the spindle starting up whilst changing tools, that works, failure to understand why will lead you to think you need breakers and stuff between the motor & VFD when you don't.

If you have a decent VFD it has the facility for an E-Stop data input, this will suffice on equipment of a reasonable quality.