Hi, Bethany! I am so excited for you to experience Mickey's Not-So-Scary Halloween Party! It is a boo-rrific way to spend the evening with your favorite ghouls. There are lots of character meets held across Magic Kingdom Park, as well as frightfully fun shows and my favorite Disney parade - Mickey's Boo To You Halloween Parade.
Bethany, I find that visiting Magic Kingdom Park the morning before it hosts any ticketed event in the evening is a great choice. To me, the crowds seem to be a bit lighter on those days. Since the park closes for regular guests early on those party nights, I just chalk it up to the thought that guests may want to go to one of the other parks that day to make use of its full hours. So, you may want to head on over to Magic Kingdom Park that morning to hop on your favorite attractions and save party time for the special shows and character meets.
If you are trying to fit in a visit to Disney's Animal Kingdom Theme Park without having to
add the Park Hopper option to your Disney Theme Park Tickets, then going there the morning before the party is also a great choice! Since regular park admission is not required to enter Magic Kingdom Park for the party, you could go to another park that morning and have a park hopping experience without having to actually make use of that type ticket.
No matter your itinerary plans, I think you will be in for some great weather that week. While the temps can fluctuate, the highs are usually in the 80s with lows in the 60s. I love visiting Florida in October and November because it is still warm enough to take advantage of the resort's pool. The evening are usually so pleasant, sometimes just a tad chilly enough to stash a light jacket or sweater in my bag.
I hope this information helps you plan for your trip! Please let us know if you have any other questions.
Brandy