Hi Christine,
Wow! It sounds like you have a fun vacation planned. I am a little bit biased, but I definitely think you would enjoy
Mickey's Not-So-Scary Halloween Party as an adult. Not only is Mickey's "Boo-to-You" Halloween Parade unique to the event, it's one of the best parades of the year.
Happy HalloWishes fireworks show is my personal favorite and seeing so many Characters all around Magic Kingdom park is so much fun! You will also have very little wait time for your favorite attractions during the party, especially in the earlier hours when families with younger children typically spend time trick-or-treating and meeting Disney Characters.
You may certainly arrive to the party late if you wish. That said, there is plenty to do to fill your whole evening with fun. If it were me, I might plan to switch my dinner reservation to another time to make the most of the evening.
Please let us know if we can help you with any other questions as your plan your magical trip. Thanks for visiting the Disney Parks Moms Panel!
Andrea U.