dear sir, i'm in tokyo now just took the train the same everyone is saying, the biggest inhibitor for you is the time it takes to get from rice field narita to tokyo, but if i you plan carefully it shouldn't be hard. If you scan the airport most service desks have someone who speaks some english or at least will understand enough to direct you to someone who does. I needed to double check my directions for the train and there was an attendant next to the ticket terminals who spoke near fluent english so don't feel too much like a fish out of water... i barely speak any japanese and i got along fine. I'm not sure where the concentration of bike shops would be but i do know there is a fair amount in the harajuku yoyogi koen area.