If you have kids, you pretty much have to do MK first. I can't imagine going to any other park first. After that, we try to take advantage of EMH when possible, but we seldom go to only one park in a day. We like doing one park in the morning, taking a break at the hotel and another park for dinner and the evening. It makes every day feel like 2 different days. As for water parks, we usually plan a day right in the middle of the trip for a water park. We consider it a down day. We sleep in since we don't have to be at the park til 10 or so, and then just relax and swim all day with a nice dinner at the hotel later. Then we're all ready to go again the next day, and it feels like a whole new trip.
Ok, so let's see... I turn every day into two days, and each week becomes two weeks, so by following my plan, you will actually feel like you were there for 4 weeks. What a deal!