I lived in Puerto Rico in the later 90's and used to island hop on the weekends as much as possible. I've been to at least half of the major islands while I was there, of course at the time Cuba was still off limits and Haiti has always been a little on the dangerous side. San Juan is always a nice stop, lots of shops in old San Juan and El Morro right there. It's been awhile since I've been to the DR, but it's fun place too. Back then while we were there we always returned with our one box limit of personal use Cuban cigars because they were really inexpensive there.

It sounds like a great trip, you should have a lot of fun!
!BBH