Don't eat.
Kidding...
Your ideas are good ones, and I don't think you'll have any problems, your budget is good.
Eat one big meal a day - and then snack as healthy as you can. If you want to do sit down meals, lunch is cheaper than dinner.
Breakfast in the room, followed by an 11:00 snack, a 3:00 sit down lunch, a "leave the park" snack and popcorn in the room, would be my ideal budget day. Although you could do counter service and probably save a few bucks.
Pack some snacks to bring into the park with you. Granola bars. Cliff bars. Dried fruits. String Cheese. We always haul in fruit snacks for the kids. Some people haul in entire meals - sandwiches, pop, chips.
Watch the snacks you buy at Disney. Popcorn, pop, Mickey Bars, Beavertails and Dolewhips can put a dent in your budget - especially if everyone needs their own. There can be the tempation of each snack item looking better than the last one, and to try a little of each (especially wandering through World Showcase)
If you aren't "big eaters" you can split a lot of Disney portions.
Drink lots of water - bring it in with you and save a couple bucks a bottle.
Don't order alcohol with your meals - its expensive.
Know where the good deals are. If you have time, going over to Trails End is supposed to be a great value. The rotisserie chicken meal at Cosmic Rays is another meal a lot of families find is a good bargain.
Consider vouchers. We aren't a voucher family, but a lot of Dis-ers swear by them.
If you have a car, consider eating offsite. We aren't an offsite family (I haven't been in Florida other than Disney property and the airport and the trip in between in fifteen years - except to visit friends in Tallahassee), but once again, a lot of DISers swear by restaurants off site.