We recently chartered a 39ft cat (our first) in BVI's through Sunsail this past December. I sail a 35ft mono and had similar concerns / worries. Prior to the trip, our neighbor at the local marina offered these words of advice: if you can figure out how to sail a monohull and you know how to drive a car, you will be fine on a cat in BVI's. He was absolutely correct. By the time, we left the breakwaters of the marina, I was fairly comfortable in maneuvering it. Picking up a mooring ball or docking was a LOT easier than with a monohull. Needless to say, the extra space inside and outside was a huge plust for us and the guests.
One word of advice / caution: once the admiral sails a cat (with all that extra space & storage), you will have a hell of time getting her back into the mono. That was the only reason that I still regret chartering that damn cat . . .
Qui craint le danger ne doit pas aller en mer.
He who fears danger should not go to sea.