Dominica is one of my favorite islands, but it is off the beaten path for land visitors and only the hardy eco-adventurers tend to go there (plus the several thousand med students). Making a living or breaking even on a B&B is going to be tough. I have an acquaintance with a chrter cat who is building the same thing right now, plus owns rights to one of the waterfalls there. If you wish, I can put you in contact with him.
The sail from the USVI to Dominica in one straight shot is doable on one tack in just about any set of the trade winds, although it will better with a northerly component. The seas are going to be against you and the trip won't be a smooth ride, but perhaps a bit better on a cat.
Call it 260nm from Charlotte Amalie to Portsmouth - a good sized cat against wind
and waves could make 5 knots, that means 52 hours of sailing - just over 2 full days.
I usually take a more leisurely approach as Teej has outlined (my average is 6-8 knots on a relatively fast boat:
North Sound BVI to Marigot, St. Martin to clear in, then on to Grand Case
Grand Case to Ile Fourchue or Anse Columbier, St. Barths (clear out of St. Martin)
St. Barths to Pinney Beach, Nevis
(arrive dusk, depart dawn)
Nevis to Deshaies, Guadeloupe
Deshaies to Anse de Bourg, Iles des Saintes, Guadeloupe (usually calm to Vieux Fort so one needs to motor
, then get hit with 25 knots for the hop across)
Finally, the short hop from the Saintes to Portsmouth.
Much more relaxing when not on a schedule.