1. Sounds too good to be true
2. Quite possibly.
3. Stock end-to-end solution from a bicycle manufacturer. Trek, Giant...
4. Buy a motorcycle instead. Did you _ever_ go > 25mph on a bicycle?
5. Watts are what moves you. Higher voltage solutions are usually mode efficient.
9. Controller is a piece of electronics that controls the motor. You don't have to think about it if you went with me on (3).