You don't have to have a PS, but it helps if you know about what time you would plan on eating. I don't know the number, but I'm sure someone else here does.
Characters are there for all meals. We saw Minnie, Pluto, Goofy, Chip and Dale. They were in seaside garb which was very cute. Ariel is there sometimes, but not everyday or all day. We didn't see her at all. If she's one you really want to see you might call and ask what time she's generally there.
I really liked Avalon Cove. The food was good and the price decent for as much as you get. If you're a Disney Club member you can now get a 10% discount with your club card.