Re: Just getting started
Unless you plan to change the rear wheel/hub there's really no advantage to installing a shift kit. You currently have a single speed rear hub so the advantages of being able to use the bicycle gears will be lost and the complexity of the shift kits makes adding one redundant in your case. Why are you set on eliminating the engine side drive chain? There are hundreds, thousands of them out there running just fine.
With that said you do have a great foundation for a motorized bike. Keep us posted on your progress and that custom springer you're going to build.
Good luck, have fun and ride safe.
Age and Treachery Will Always Triumph
Over Youth and Skill & "Charlie Don't Ride"