You can definitely purchase anything you want to on island. It will be more than at home, but not substantially more. For that large a group, unless you check a large suitcase, I really don't think you should even consider trying to bring stuff from home, as it will be a drop in the bucket.

Regarding places to buy groceries on island, for a large group, you should consider Cost U Less, which does sell in bulk. Not necessarily for meat, but for soda, etc., etc. As far as grocery stores in general, as of June of this year, Super U in Marigot seemed to have the best prices for meats on sale and wine was available for just stupid cheap prices.

As far as restaurants, 22 is a really large party for ANY restaurant on island. No way you should consider going anywhere without a reservation, which I assume you already know. If you are looking for a place with a large variety of different foods--including upscale French-- for that large a group, I would recommend Dreams, in Nettle Bay. For someplace that serves a wide variety in a real casual setting, would recommend Pineapple Pete. I would also recommend that you check out Captain D's, which is right by Royal Palm, and get several orders of carry out, as they serve great BBQ for a cheap price.