We're taking our third holiday trip. We love it at WDW at that time of year. We arrive on 12/22 and leave on 1/4.
The weather is very unpredictable. I like to bring layers of clothes, rather than a bulky, heavy coat. Gloves and hats are also good to have on hand. Rent a locker if you want to store them.
Check your calendar, and make Priority Seating reservations at either the 120 or 60 day window, whichever is applicable for where you wish to dine.
The Magic Kingdom is fine if you get there early on Christmas morning. It's not until about noon that it gets crowded. By parade time, it's cheek to cheek. The other parks are usually empty by comparison.
Take your time and enjoy the beautiful decorations. Visit the Grand Floridian and the Wilderness Lodge for a special treat.