Quote Originally Posted by A_Camera View Post
That is only true if he ALWAYS wants to have the stepper energised and always holding. That is not always desirable or even advised. So unless you absolutely certain that he doesn't care about enabling/disabling the driver it is indeed necessary to switch the enable signal also. Regardless of which, there is no harm in switching it, but there can be harm in not switching it.
If you'd looked at the relevant photo, you would see the Enable on the driver has nothing connected to it, plus there is also the post stating he doesn't want the axis to become disabled to avoid the axis dropping, so connecting the enable is not needed.

GND is the same as STEP - , DIR - and EN -. It is better to connect those to the same - output as the one providing the control signals. Again, it would do no harm and we know too little about his design and implementation.
Not on the existing step source, as again, the photo shows differential outputs.
However I did think about this earlier, as the alternative controller may not have differential outputs, so some thought may be needed in that regard.

That's why I said that a small signal relay needs to be used, not a contactor. You talk about a contactor which is designed for high voltage and current.
All relays, apart from specialist relays have minimum switching currents. It is not something that only applies to contactors.
Good relay manufacturer's will publish the relevant detail in the datasheet.