I am all about the Dining Plan. I have budgeted it different ways. Disney is making money off me when I use the Dining Plan, but it is worth it to me so I don't have to constantly be concerned about the food budget the whole time I am there.
If you all do not want to take the time to sit down for any meals, then get the quick service plan. If you want to do the sit down restaurants, tips are not included in the table service meals, so you will need to budget for them. Also, some table service meals are two credits, so you will want to check that out as you are making your reservations.
You may want to budget additionally for drinks to have in the park and you may want to eat breakfast in your hotel room. If you are flying, there is a delivery grocery service called Garden Grocer that will deliver to your resort. (there is another grocery delivery service, but can't remember the name.) Otherwise, you may want to bring a couple of cases of water, so you can bring everyone can bring a bottle of water into the park each day.
Our favorite sit-down restaurants:
Crystal Palace (buffet, Winnie the Pooh and Friends character meal)
Ohana (any meal is great, but they do have a character breakfast as well)
Kona
Hoop De Do Review is a good bet for kids. My niece and nephew loved it when we went.
Hope you and your family have a magical time!!