We just picked the most important ones and asked Mackenzie which ones she wanted to do. She wanted to do Candy Land which was a blast and they had carnival games, cotton candy, and snow cones. She wanted to do Halloween because she was in the hospital and didn't get to trick or treat last year. She wanted to do the Big Splash Bash but that was our least favorite. It was hamburgers and hot dogs by the pool with a few games but could have done without that since she loves to swim on her own and we did that every day. She loved Christmas and I would encourage you to do that one if time allows. They make the kids feel really special and they all get to pick out gifts from Santa, decorate cookies, there is a Christmas parade, a craft, the dinner is a nice holiday meal with turnkey and all the trimmings. We did Village Idol but that too unless your kids really like performing isn't a must do but it did bring tears to our eyes to see all of the kids perform their talents. The princess and pirate party was fun too! We left before Mayor Clayton's birthday party but we got to all of her must do's. We were able to do the Magic Kingdom parade, Wishes, and fireworks after the Candy Land Party. We just made sure that we came back in enough time to get naps and dinner, did the Candy Land and then went back to the park for the evening. That night it was open until 2 am but we stay until about midnight. We also did the evenings parade, etc. again on one of the nights we didn't do the party because Mackenzie wanted to see it again.
There is so much to do that you just have to figure out what works best for your family and do the things that are important to your kids. We have seen Fantasmic and the Epcot night show before and while they are good my kids didn't think they were a must do and wanted to do some of the other things more.
No matter what you decide you can't go wrong and you will have an amazing time!