Hi Amanda,
Firstly, I think that it's great that you are planning your upcoming trip so early - planning is almost as much fun as the trip itself, in my opinion.
I can highly recommend
Disney's Keys to the Kingdom Tour. Both my Husband and myself have done the tour during previous visits to the Walt Disney World Resort and thoroughly enjoyed it.
I am not 100% certain if this tour is available to book on New Years Eve. According to the Walt Disney World website, at this moment in time, it is currently possible to book the tour for dates up to and including October 29, 2016. What I would recommend that you do is to check the dates that the tour is available to book on the Walt Disney World website in say 6 - 8 weeks time. If the tour is available to book for December 31, 2016, there is a very good chance that the tour will also be offered on December 31, 2017.
My family have visited the Walt Disney World Resort for a 2 week period over Christmas and New Year twice in the past few years and both times, the crowds thinned out considerably from January 3, onwards. As you are planning to stay up until January 8, that should leave you a good few days at the end of your trip to experience the parks with only moderate crowds.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma