I am going in December too! The first two weeks, hopefully.
Well sunya, let's see...
Dinner at Liberty Tree Tavern is a great idea! The food is delicious and the character outfits are reallly special! As for MVMCP, it's good to arrive early and get a good spot for Celebrate the Season show at the castle stage. It's awesome!!! There's another great show at the Tomorrowland Theatre, just check the times when you arrive. The Country bear christmas show is also great, but it runs everyday, not only during the party, so you don't have to worry about it. I think the MK is open until midnight, but I am not sure. Anyway, be sure not to miss the parade, I think they have it twice at each party. And of course, the special fireworks. If you can get your family picture taken early, it's better, as the lines tend to get longer and longer as the party goes. The cocoa and cookies are good, too! (well, at least for me...)
As for other Christmas stuff at WDW, I've heard that the Grand Floridian has a life size gingerbread house, which is really beautiful. There are also the Christmas stuff at Epcot, like the Candlelight processional and all the christmas storyletting at world showcase which is very interesting. Let's see, what else? Well, the carolers at Epcot and Downtown Disney are very good too, so if you have some spare time, check it out!
I hope I've helped you... If you have any questions, just ask!!!:xmas: