We had a Moorings 4000 (really a Leopard 40) for 8 people in the BVI last February. It was a _little_ tight for 8, but doable. It would have been great for 6, and probably overkill for 4. Our biggest problem was having too many people for one dinghy load. The large cockpit and saloon on the same level was really nice.
RealityCheck is right on marina's--I'd be surprised if you stayed at more than 2--your charter base and maybe Leverick Bay.
It was our first experience on a cat, and the Leopard 40 sailed much better than I had expected based on the general reputation of cats. It was set up to handle all sheets from the helm--if I had any complaint it was that I had guests that wanted to help sail, and it was really setup for single handing. Except for the main halyard. I worked them pretty hard on that :-)
By the way, if you haven't already found it, TravelTalkOnline is the place to go for BVI info. Lots of locals hang out there.
s/v Dancing Days
Lewisville Lake, TX