I Love Disney! taking a 5 year old is a very very good age, he will love it and get to enjoy almost all the rides on the parks!
Christmas is an extremely busy time of the year for the parks, so will need to pack a LOT of patience!
I will send you a private message since I do have tons and tons of recommendations, especially if you have never been. ( I have gone 3 times in the last 2 years).