we did what many others did - park for the morning, head back after lunch for swim/nap, then back out for dinner/evening. My kids aren't bothered by the night stuff or fireworks, but we did bring glowsticks and bracelets from the dollar store at home to let them have for the darker rides and at night time.
We order from Garden Grocer all the breakfast items and snacks, and would pack up the stroller bag each night before going to bed so that in the morning it was just get up, dress, head out the door - kids can eat breakfast while watching tv as the grownups are showering and applying sunscreen
We found buffets to be kind of a pain with the small kids, because you are always back and forth, sometimes waiting for a character and missing out on getting food, etc. For us, we preferred table service like Garden Grill where the characters AND food come right to your table
For fastpasses we skipped the 'adult rides' like mountains and coasters, and used our FPs for things like Peter Pan and Tomorrowland Speedway. You can always do Rider Switch for grownups rides (we did this for Soarin').
We tried to take it easy, not see everything and just follow the lead of our children - if they wanted to stop and watch water fountains for 20 minutes, we just did. It was so much more magical than rushing around and missing everything that is so interesting to look at! Remember: there will always be another trip!