Feedback needed on itinerary

I’m new to this forum so I hope I’m doing this right.

We are headed to the US in December and January 2018/19 and will be landing in Orlando at about 6pm on the 16th of December and fly out on the 20th (probably early). However we will coming back on the 31st (around 4pm) and fly out at 8pm on the 5th. We are hoping to cover all four Disney World parks plus the two Universal. I know, a bit hectic but we think it’s possible.

Here is my plan:
16th, 17th, 18th, 19th in Universal staying at a Universal Express Unlimited hotel. However on the day of the 18th getting an Uber to Magic Kingdom for the day and going to the Christmas Party (sounds like a unique experience).

31st - 4th staying at Art of Animation for the whole time with park hopper tickets.

This is basically our budget with the option to add on things like After Hours and dessert parties to make use of the time better.

Cheers for the advice.