With the new airport open flying directly to St. Vincent is the way to go to. I can't comment about the charter aspect as we always do a crewed charter. You'll have plenty of options on where to go for a week charter.
Kingstown has the best market (fruit, veg, sauces, spices) in this part of the Caribbean; their fish market, located nearby, is also very good. There are supermarkets on St. Vincent and a decent small one, Knights, on Bequia after that the pickings are slim.
I would recommend a full day ( two nights) on Bequia. Myself, between Palm and PSV, I prefer Palm. Nice thing about a stop at PSV though is that you can go over to Petit Martinique and take a nice hike around the island. Miopion is also right nearby for some decent snorkeling (hour or two tops).
It's a great area, you'll love the sailing.

Drink all day at home, your friends worry about you; do it on vacation and they say "what a good time you're having". Save your friends needless worry, travel more!