Hi Melissa! In case you didn't know, you'll be able to enter the Magic Kingdom (MK) as early as 4:00 p.m. with your Mickey's Not So Scary Halloween Party (MNSSHP) tickets. If you'd like to have your character dinner in the MK, my recommendation would be
The Crystal Palace. Here you'll be able to dine with Pooh, Piglet, Tigger & Eeyore (characters subject to change). The other character dinner located in MK that you may want to consider is
Cinderella's Royal Table which is hosted by the Fairy Godmother.
Other nearby character dinners are
Chef Mickey's - located at the Contemporary Resort and
Cinderella's Happily Ever After Dinner - located at the Grand Floridian.
Dining locations are very popular on MNSSHP nights so make sure you call right at 7:00 EST 90 days before your vacation for your best chances to secure your favorite restaurant at the time you desire.
Good luck! Diane :)