You can also see the full Manhattan bus map at http://web.mta.info/nyct/maps/manbus.pdf

From THoR, the most useful buses will be the M14A and M15 (especially M15SBS). The M9 is less useful. The M21 has a good route, but runs very infrequently. There are lots of iPhone apps that can help you see when the bus is coming. I like busbusnyc, which shows a simple, nearly real-time map of all the buses in your vicinity.

Note that between the BDFM and ACE platforms at West 4th there are elevators if you have trouble with stairs. The F platforms at both Delancey and 2nd Ave are two full flights below street level and there are no elevators, although there is an escalator up to the north side of Delancey from the downtown F platform, and to the south side of Delancey from the uptown F platform. You can also get from the street directly to the uptown M platform directly with just one short flight of stairs if you enter the station from the entrances on the north side of Delancey near Norfolk (in front of Children's Place or Banco Popular). But note that the M usually only runs into Manhattan on weekdays.