Start with the motor, nameplate horsepower and amps, application (fan, pump, conveyor, winder, extruder etc). How will it operate, (via local pushbutton or remote controls or both). Input voltage, length of motor leads. Will it be an overhauling load. What are the present conditions where it will be installed, (indoors, outdoors, dirty, etc). Will it require bypass contactors for maintnence or emergency operation.
That should get you started.