Re: Custom built, legal and self-propelled 'car'
Welcome to this fascinating and at times maddening world of motor bikes. You are now being gently drawn into the realm.
As mentioned ask at your local D.M.V about what they consider legal. Usually if you have three wheels and pedals hooked up to the wheels so you can pedal it manually it is considered a bicycle trike. I believe that you are allowed 750w of electric power and 50cc as the engine size.
Best of luck and if you ask for information give it a day or two for people to see it and answer.