I'm not sure how difficult it is to get ressies --I called about 85 days before our vacation and got my daughter in on our preferred day with no problem at all. She had a great time!
As for a deposit -- they do take down your credit card number, but that is not charged until 24-48 hours before the Tea Party. If you want to cancel, call and cancel at least 48 hours in advance, or else your card will be charged.
HTH!
Linda