Hi Stacey!
You've picked a great time of year to visit Walt Disney World,the lights, festive decorations and all the delicious treats make the holidays extra magical!
Mickey's Very Merry Christmas Party is a great way to get into the holiday spirit, snow lightly falling on Main Street USA and Cinderella Castle literally dripping with lights is an incredible sight. Mickey's Very Merry Christmas party has a special version of the very popular Wishes firework show called Holiday Wishes and it is every bit as magical as the regular Wishes. Plus, there is also a special parade that can only be seen during Mickey's Very Merry Christmas Party or the week of Christmas, Mickey's One Upon A Christmas Parade.
The Park Hopper option is a great add-on and help you to see much more of Walt Disney World if time allows. I just want to caution you that many guests, especially if you are traveling with young children, find that much transferring between parks can take up a lot of time. I usually suggest visiting the parks at least one day to find out if you feel that it is beneficial to your vacation. The Park Hopper option costs $59 no matter the length of your ticket (except 1-day Magic Kingdom Tickets is $34 and 1-day Epcot,Animal Kingdom or Hollywood Studios is $39).
I hope this helps and please let me know if you have anymore questions!
Best Wishes!
Mandy