Congratulations!!!!

You will have a great time! I don't think the characters make regular appearances except for at the brunch, so if you really want to see characters, then keep that in mind. I don't know what the cost is for brunch, but the minimum order charge per person at dinner is something like $63 (basically the same price as a one-day admission.)
Oh, and I would suggest that you don't tell anyone at the club how you got your invite. Members are not supposed to donate entry to auctions. I actually got outbid at an auction, but my mom knew the donor and when she told him what a Disney freak I was he invited us to go. He recently told my mom that they received letters that said donations of this type are a no-no and will jeopardize your membership. I just would hate for your generous donor to get in trouble, so be careful!