If it is a tiller model, you would need the starter motor, mounting bracket, solenoid, battery cables, and a push-button switch with related wiring. If your motor lacks a toothed flywheel, you would need that, too. If you want to add charging capability to keep the battery topped off, you would need to add a charge stator.
For part numbers, check the parts listings for an electric start version of your motor at any of the various sites with online parts listings.