The two weeks leading up to Christmas week are very light. Once the week of Christmas hits (which would include your visit) the crowds get heavy. But with careful planning and a good outlook you can still have a good time. Be sure to get there at opening to maximize your time. Take an afternoon break, when the crowds are at there highest. And go back in the evening. Use FP to your advantage. And relax.
We were there over New Years Eve and while it was very crowded we had a fun time.