My wife and I are going on the Zaandam April 16th as well. We have been on this itinerary before. I suggest you visit the Bath pools in Virgin Gorda. We took a ferry from Tortolla and had a great time.
In St. Thomas we rented a car and drove to the other side of the island to a very nice beach next to a marine park.
Half Moon key is to die for. Great place for snorkeling and relaxing.
Any questions? Shoot me an email.
PorscheOtto