We just got off of Infinity. This was our second cruise on Infinity. We love the ship. Very good food and very nice decor on the ship. (Elegant decor not flashy like some ships.)
We have been to some of your ports on different ships. St. Thomas is very commercialized but still a very nice stop. You can take a taxi to downtown Charlotte Amalie to do a lot of shopping. If you take a tour that takes you to Megan's Bay, you will love the blue water. You can also take a tram ride up the side of a mountain that will give you a great view of the cruise ship. We took an island tour on Barbados and Grenada. Barbados was very nice. Grenada, at the time, was totally uncommercialized and one of our favorite ports.
The itinerary you mentioned sounds good to me!