We have done this several times from St. Thomas and enjoyed it. I strongly suggest you get the Pavlidis Cruise Guide to Puerto Rico and a chart. I do not recall if CYOA provides these or not. They also had some other requirements so you may wish to check with them.

If you are only going for a few days, I would just go to Culebra. Regardless, you will need to check in with Puerto Rico customs either by phone, or possibly using CPB Roam. You do not have to check back in to the USVI on the return. Be aware that at this time of year, the northern anchorages, Tortuga on Culebrita and Flamenco on Culebra may not be a good idea if there is a north swell. Other options would be Dewey, Dakity, or Almodovar. There are moorings in a few places but I suggest you check the depth before picking one up as a number of them are in very shallow water.

It is also likely that the trip back to St. Thomas will be a slog motoring into the wind for the better part of a day. If the wind comes up to 20 knots or so, your crew may hate you. If you go to Vieques, on the return from Esperanza you will motor east for about 10 miles before you can head to STT. Again, in the winter months if there is a northeast fetch to the wind it will be a long day motoring as well.

Another option if you have a reasonable wind/sea forecast could be to go to St. Croix (Christiansted). From the south side of St. John it is a reach both down and back.