I would recommend Fantasmic over Illuminations if you have to pick one. You could start a thread on that, because it'd probably be a pretty even split.
Also as far as parks, what does EasyWDW say about Wednesday at Epcot? That would probably be my focus and then focus on DHS on Saturday.
Please come back and tell us how much fun you can have without prebooking fp+, we've done it. I know it can be great.![]()
I was also told not to miss Fantasmic. I'm leaning towards this over Illuminations if I have to pick. We will definitely be seeing the Hallowishes and Wishes fireworks.