With the limited time you'll have in the park (8 hours total, with the MHP ticket), I wouldn't waste time eating dinner during the party. If anything, I would eat in the three hours before the party starts. The 5 hours of the MHP will be your only chance to meet special characters, see Halloween Screams and Paint the Night, ride some rides with shorter lines, etc.
I don't know what time Goofy's Kitchen closes that day -- sometimes it closes at noon, sometimes at 1 p.m., and sometimes at 2 p.m. If it closes at noon, I would try to get a breakfast time that's a little bit earlier than 11:20, just so you don't catch the characters as they are winding down and heading out.
If eating dinner during MHP is a must, Plaza Inn is good -- for both a meal and dessert.