As others have noted, Christmas week is the busiest of the year at WDW. I second the recommendation to be there for rope drop. If you are staying on site I would plan on taking advantage of the morning Extra Magic Hour and do as much as possible before the crowds build. It will require getting up very early but it will be the time of the lowest crowds. If (when) the crowds grow too overwhelming, head back to your resort to relax and decompress.
Wishing you a visit!
Wishing you a visit!