St.Thomas & St.Maarten have the best shopping!
In St.Kitts consider the "St.Kitts-Nevis Sailway". Nevis is "Travel Brochure Pretty" and the catamaran crew is great and very helpful. There's a snorkeling stop on the way to Nevis -- lots of fish.
Antigua has 365 Beaches. Gee, you could go to a different one every day for a year! Seriously, I love the "baby powder" white beaches of Antigua. Just pick one -- you'll like it!
Barbados has good water sports and there are always the tours to the caves and rum factory.
You itinerary is great. You'll have a wonderful time!
Have Fun! WSEA