Part of your preparation should be to obtain a scope plot of the inrush current response. An NTC is rated to absorb a certain level of energy during the initial transient event, and a datasheet would provide an example of that energy capability in the form of charging up a capacitor (as that is the most common usage).
Another part of the prep is to determine what minimum current is needed to start the motor, as it may be that even using a constant current power supply, the start-up current required must be larger than the steady state current, so you won't be able to insert more than a certain maximum series resistance.