Hello Tasha!
Welcome to planDisney! I love that your Park energy matches mine.
Mickey's Very Merry Christmas Party is a lot of fun but since these tickets let Guests enter Magic Kingdom Park at 4 pm it only seems right that one maximizes their time fully. Since you are an Annual Passholder you have the luxury to enter even earlier and I'm very excited for you.
Having your family drop you off at the Ticket and Transportation Center and then having them return later is a great idea. You only have to
pay for parking one time for the day. That pass is good all day and valid for all four theme parks! Don't lose it! However, they say that spaces are not guaranteed if it is crowded but Magic Kingdom Park's lot is huge and could fit all of Disneyland Park in California in it. I think they will be fine for that day especially as specially ticketed events have a limited attendance.
Since you will already be in the Park when the party is starting I recommend you get your party wristband from the marked locations in Magic Kingdom Park. Starting at 4 pm you can just head over to the wristband pick-up location at
Mickey's PhilharMagic in Fantasyland, Tortuga Tavern in Adventureland, and the area across from Monsters, Inc. Laugh Floor. I prefer the Monsters Inc. Laugh Floor location as it moves very quickly due to how they set up the flow.
I hope this helps and you have a fabulous time!
Happy Planning!
-Nimmy