The cruise lines are generally fairly forgiving if you want to bring your own sodas onboard. On our cruise, I brought a 6-pack of 16-oz Cokes, and my wife brought a 6-pack of 20-oz Pepsi, in our checked bags. There's an empty fridge in every room so we were able to keep them cold. Princess is a Coke-only company, so if you want Pepsis you'll _have_ to bring your own.
You'll love the scuba. I was certified and lived in Jamaica 35 years ago, and we went diving every weekend. Absolutely beautiful on the north coast. Got recertified because they changed the dive tables and equipment since then. Now I can dive on any cruise <g>.
Dunno if anyone told you, but Cruising Is Addictive. Says so right there on Page 1 of the excellent Berlitz book Cruising and Cruise Ships 2005. We took our first for our 20th anniversary in 2000 and I've managed to take 6 more since then.
I've been on a few HALs and a few Carnivals but definitely think Princess is the best.
Oh...to answer one of your other questions - there will be kids onboard, but most of the time they'll be in the kids center or in the main pool. There's at least one adults-only pool too. So hopefully they won't give you too much grief.