Hold your arm out to you side. I refused to get into an argument over levitating arms. Actually both take energy since your accelerating and decelerating masses of your body. Thats probably the central thing confusing you. Ah, now I see.
Energy total yes.
Energy on the ship, no. Furthermore, prelaunching only works for acceleration, not for decelleration. Agreed, but then you can say the same thing about photon sailers. I think bottom assumption was a hydrogen atom every cubic centameter or 4. Don't understand you question.