Hi, Courtney! Thanks for the question! I know what it's like to travel with a family at that age. No, I didn't get a Minority Report-style vision into your upcoming trip. Rather, in spring 2010, our kids were 5 years old and 18 months old when we went to Disney World.
The best starting point for planning out days is TouringPlans.com's crowd calendar. Overall, the crowd levels will be minimal during your trip.
Last year when my boys were 18 months old and 5 years old, they really enjoyed character experiences. Some of our favorites were
Crystal Palace,
Donald's Safari Breakfast,
Cinderella's Royal Table and
1900 Park Fare.
The Halloween Party is projected to happen several nights during your trip. I'd recommend going on the last night of your trip on Sun., Oct. 2.
One more suggestion? Our youngest son was very active at 18 months old. He had about a 2 minute shelf life in a stroller and then would feel the urge to go bipedal. At Disney World, we countered that impulse with a toddler hiking backpack. He loved riding in it, strapped to my back, and he would even take naps in it. It made a world of difference. The one we got was the REI Piggy Back (got it off of Craig's List.)
Let me know if you need any more help!