I went that exact same week last year for the first time. Crowds aren't too bad, especially for Mickey's Christmas Party. The crowds were exceptionally low the night I went. Most of the crowds gather for things like the lighting of trees, parades, and the candlelight processional.
Crowds for MGM's light show were probably the worst that we saw but after an hour the crowd disperses and it's not bad.
The ride wait lines varied, and weren't as crowded as the xmas events. Most we got on in 15-20 minutes or less, but some of the more popular & new rides like Soarin were an hour. Just get fast passes early in the day to rides such as that and you should be fine.
If there's a certain restaurant you want to eat at, make reservations. Almost all the character dinings & unique places were booked already when we got there, but I think it's like that all year. Have a good time =)