It depends or the number or ports you go to and even which ports you go to that will determine how much you can bring back duty-free. If you go over the limit you simply pay the duty on the excess. If you ship it back I believe that you have to pay duty on any and all of it.
Shippiing alcohol through the mail is illegal in many states.
The money you save on the purchase in the Caribbean would be wiped out by the shipping and customs costs anyway.
Why not just buy it at home?