We were there in November and had no issues with overbooking. We're actually leaving again on February 3rd because we had so much fun!
In terms of tipping, we would hand the bartenders a tip like we were shaking their hand. For the waiters/waitresses, we placed the tip under a glass or plate. As far as I know there isn't a policy at this resort but we didn't want to chance it.
Insulated mugs are so important because the glasses you are given are really tiny plastic ones. It saves the number of trips to the bars and keeps the drinks colder longer.
Reservations can only be made on the day you want to eat there. Be sure to ask when you check in which nights the two ala carte restaurants are open as they are open on opposite nights. On the day of you just go to the front desk and let them know if you want the 6:30 or 8:30 seating. We never had a problem getting a reservation and never had to wait in line early in the morning to do so.
Have fun! You'll definitely enjoy this resort.