I think the Boston Duck Tour is worth considering. Again, having been to Boston several times, I enjoyed this. You can see their website here
. Tickets are available either online, or in person. They offer two locations for purchasing tickets. The first one is at the Museum of Science, and the second, which is probably more convenient for you, is the Prudential Center shopping mall.
If I remember correctly, I think the duck tour is about an hour and a half. Not sure how much time you have in Boston, but that's something to consider when purchasing your tickets.
Sorry I can't answer your other questions. We always take the T instead of taxis. The T is their local subway system.
2007 - Majesty of the Seas
2009 - Enchantment of the Seas
2010 - Freedom of the Seas