That's not a great choice of motor for the G-540, which only goes up to 50v. You won't get much speed out of it. It really wants about 80v, due to its high inductance. If you haven't bought the motors yet, find other ones. If you haven't bought the G540 yet and have those motors already, think about getting three G-203V drives instead.
Mach3 doesn't need much info about the motors, beyond the 200 steps per revolution which is pretty standard.