This is Peak/Holiday time at WDW, so the rooms will be at their highest cost of the year. Also, plan on extremely crowded parks. Went once over New Year's and never again. Way, way, way too crowded for my taste. All of the parks maxed their capacity by 10am and you knew it. Waits for some of the most popular attractions were several hours long. If you still want to go, book now. As soon as your 180 day ADR window opens, call and make ADR's for all of the sit down restaurants you want to dine at. Can't tell you how many times I saw people being turned away restaurant after restaurant with no ADR's and the place being completely booked for the day.
If you are looking to go when the resorts and parks are decorated, then I'd suggested going between the day after Thanksgiving through the week BEFORE Christmas. Much less crowded and you can really enjoy all that the parks and resorts have to offer at that time of year.