I have done this trip many times, both R/T out of St. Lucia and one way SL to Grenada. Last time was 2 years ago R/T start and finish in SL out of Rodney Bay. One thing I can tell you about the Mooring ops out of SL is that it has always been first rate with spot on local intel. They always gave us good info on where it was safe to stop and where you might want to avoid. One gem was a small bay with a great little french restaurant. They had their own moorings and it felt very safe. Others here may recall the name of the stop I just don't have it right now. In any event it is north of Kingstown but south of Cumberland. We were able to easily reach Rodney bay the next day. You could use it as a stop both up and down without trying to kill yourself reaching Bequia. When you get to Bequia to clear in you can contact African (associated with Moorings) who was very helpful in getting a ball and general info. BTW as an aside I never got the attraction with Bequia!!
For C&I you can clear in and out of Bequia pretty easily, never had a problem there. If you are in Tobago Cay and want to check out there you needed to go to the airport at either Union Island or Canuoun.
Hope this helps, but remember too that this info is 2 years old.