Hi Stephanie,
Welcome back to the Disney Parks Moms Panel and I'm happy to offer my suggestions for your upcoming trip. Although dates are not released yet for
Mickey's Not-So-Scary Halloween Party, my best guess is the party will take place on the 29th and 31st during your vacation, and perhaps another night as well. Be sure to keep an eye on the Disney Parks Blog and the link I provided for release dates.
10/27: Magic Kingdom
10/28: Disney's Animal Kingdom; Pirates & Pals Fireworks Voyage
10/29: pool day; Mickey's Not-So-Scary Halloween Party
10/30: Epcot
10/31: Disney's Hollywood Studios
11/1: Magic Kingdom
You'll notice I didn't suggest visiting Magic Kingdom ON Halloween, as I anticipate the crowds being heaviest on this party date. If staying on-site, you'll want to take advantage of Extra Magic Hours once they're released, so your itinerary might need a bit of tweaking as times come available. I also love to visit Magic Kingdom on our first and last days to truly take in every bit of magic from start to finish. There's something very special about catching the reflections of Wishes nighttime spectacular in your children's expressions. It'll likely become a lasting memory of your Walt Disney World vacation.
Have fun planning, Stephanie, and feel free to ask me anything else coming to mind.