It's our first time too and we're going at the same time (December) as you. I see no one has replied so while I'm new to cruising too I have done a lot of research so perhaps I can help.
First about pre-booking excursions. The general thought is if they are short excursions it is best to wait and book them onshore because you can get a better price. However, if you arrive back late the ship will leave without you so for long excursions the thought is it's best to book with the cruise line because they will either wait for you if your excursion is late getting back, or they will make sure that you get to the next port. And the big surprise for me was to pack an extension cord (not a surge protector) because there is usually only one or two plugs in your room. I would research online your question. You'll get lots of good tips. Have fun. Maybe we'll cross paths and not even know it.
Carnival Triumph 12/24/16
Carnival Triumph 12/29/16
Carnival Splendor 07/02/17