Dining reservations can be made 180 days in advance, and popular restaurants fill up quickly even at slow times. Since you are staying onsite, you can make dining reservations (ADRs) 180 days before your check-in date for up to ten days of your trip. Don't wait, especially if there is a restaurant you really want.
The regular dining plan allows one table service meal, one counter service meal and one snack per person for each night of your stay. Your son is considered a child and will need to order off the kids' menu, so you might check allears.net for menus to see which restaurants have choices that he will like. For character meals and other all you can eat meals, he can eat off the adult and child buffets.
Snacks can be bottles of water, ice creams, popcorn and other items. Since you are flying, you probably can't bring a case of water with you, but you will need to stay hydrated (whether you use snack credits, pay out of pocket, or use a grocery service or take a cab to get a case of water). You can get cups of water for free from counter service restaurants just for asking. Water from the restaurants is filtered, unlike the water fountains. I think the Hess station near DTD has a reasonable selection of water, sodas and snacks - it might be worth a cab ride to not pay $2.50 for every bottle of water or Coke that you want.
Unless we are planning breakfast character meals, we usually pack granola bars, muffins, etc and eat breakfast in our room. You can also use snack credits for some breakfast items.
Our family really likes an 8 am ADR at Crystal Palace so we can see Pooh and friends, eat a yummy breakfast, and be done before MK rope drop (early diners wait for rope drop at the castle, so you have a bit of a head start if you are already in the park). You can also take a picture of your family in front of the castle without a lot of other people there.
We also like 50s Prime Time at Hollywood Studios (great fun!), Boma at the Animal Kingdom Lodge, Flame Tree at AK, Columbia Harbor House at MK, and Sunshine Seasons at Epcot.
You'll have five people in a not-very-big room, so you might want to bring an over the door shoe holder for sunscreen, hairbrushes, curling irons - whatever takes up counter space. If your kids have ipods, DSs and cell phones, you might want to bring a power strip so everyone can recharge everything.
Enjoy the planning and the trip!
Edited: You haven't been since Toy Story Mania was built. It is hugely popular with fastpasses running out before lunch every day. The same is true of Soarin' in Epcot. It's critical (especially with TSM) to be at the parks early, even if you have to drag your teenagers out of bed! Read up on strategies and attractions on the Theme Parks Board - so many changes since you were there last!
Can you tell I'm excited??
