Hi Denem916, did you check out our Caribbean Port Chat section a little further down the page? It has tons of posts about your ports. You can use your "find" feature in the upper left hand corner, type in your ports, and it will pull up all the posts made about them.
I will definitely second your choice of Trunk Bay, if the weather is nice. I cannot believe that you're not going to be in St. Thomas long enough to get over to Trunk Bay by ferry. The ferry runs more frequently from Red Hook, but it is an $18/pp cab fare to get there. This
might give you a better idea about the schedules.
In Dominica I highly recommend the Champagne Reef snorkel. I prefer doing it by boat, but they have built a catwalk down to the snorkeling area, so it's easier to get into the water. The cab fares there are pretty reasonable, so you might want to try it on your own. In Barbados and St. Lucia the cab fares are not inexpensive. The last time we were in Barbados, we went to Folkstone Underwater Park. The cab driver charged us $90/pp each way and it was not that far from the dock. The last time we were in St. Lucia, we went to Pigeon Island, and the cab driver charged us $85/pp each way, plus we had to pay entrance fees. The ship had an excursion that was $45/pp for a pirate ship. Don't get me wrong, I enjoyed the amount of time we were able to spend there and the pirate ship only spent about 1 1/2 hours and we spent about 5 hours. It's a beautiful area. In St. Kitts, we've only done ship excursions, so I'm not sure about cab fares there. In St. Maarten, you can take a water taxi over to the beach that's close to the dock for $6/pp. It's a nice beach. There's also Maho and Orient beaches, but they're about a $20-$25/pp cab fare away.
Hope this helps some and be sure to check out the Caribbean Port Chat section.