I decided to plan an impromptu trip to Disney World on the tail end of our Florida trip this fall. We'll be getting into Orlando on a Saturday afternoon, staying the night at Art of Animation Saturday and Sunday, and going to Magic Kingdom on Sunday. We fly out of Orlando on Monday evening. DS is 4, and we will be going/staying with my parents. We will have a rental car and an umbrella stroller. It's supposed to be a 6/10 (Moderate) crowd day at Magic Kingdom according to Undercover Tourist. I haven't been to Disney in years and I know a lot has changed.

Any advice/tips/tricks?
Any dinner suggestions for Saturday night and/or brunch suggestions for Monday?
Any words of wisdom on how to spend a single day at Magic Kingdom with a 4 year old?
Any advice on using the FastPass+ system?

Thank you!