Take the ASA 101 course locally and the ASA 103 locally if you can. They are the sailing focused courses and are taught on monohulls. ASA 104 is focused on systems and is important if you want to know how to take care of your charter vessel. I did all three courses in a row through the Rob Swain school, but the only real benefit was sailing in the BVIs and learning the approaches, which you have already done.

For catamaran, we had a captain for a day from our charter company show us the how-tos (awesome guy and TTOL user) and check us out. That worked fine. To be honest, sail time on a monohull and knowledge of the cruising grounds is enough. As camelot said, its not hard to learn how to maneuver and sail a cat.

Cheers, RickG