I always recommend that newbies try the road MORE traveled for their first trip. There is a reason that some locations are so popular. They tend to have more activities (something for everyone) and better infrastructure. It is easier to branch out once you know the lay of the land.
Re: water temperature. At least here in the VI, it doesn't vary much from winter (79)to summer(84). But I do not get in the water in winter because it is too cold for me. I have a friend who left the VI for Hawaii and says the same thing about the water there! Brrr.. I think the Gulf Stream is supposed to keep the water warmer in Florida?
Today is the tomorrow you talked about yesterday.