pass activiation?

I will be arriving Narita Airport on Dec 23. I plan to travel to Osaka on Dec 29. If I exchange the pass that I purchase on line at the airport, does it begin on Dec 23 , even though I don't plan to use it till Dec 29. If I buy the normal JR pass instead of first class , can I reserve the seat at the exchange office at Narita Airport for Dec 29? Is the pass begins on Dec 23 or the date of first travel on Dec 29. We are thinking using the airport hotel bus to our Hilton hotel
160-0023, Shinjuku-Ku, 6-2 Nishi-Shinjuku 6-chome, Japan. If our pass has to be activate on Dec 23 due to reserved seating on Dec 29, which train should we take to Hilton Hotel. If we decide to take the airport hotel bus, where is the closest exchange office from Hilton hotel.