Hi Cynthia,
This is a great question! Here are the big must see rides at each park:
Magic Kingdom-Space Mountain, Big Thunder Mountain Railroad, Splash Mountain, Buzz Lightyear
Animal Kingdom-Expedition Everest, Kali River Rapids, Kilimanjaro Safari, Dinosaur! (dark and scary)
Disney's Hollywood Studios-Rock 'n' Roller Coaster by Aerosmith, Twilight Tower of Terror, Toy Story Mania, Light, Motor, Action! Extreme Stunt Show (show not a ride)
Epcot-Test Track, Soarin', Mission Space, Innoventions, Maelstrom
As for the water parks, you could go to the water parks during the day and then a main park afterwards which has Extra Magic Hours in the evening. If the Extra Magic Hours are at Disney's Hollywood Studio, it will be crowded so you may want to go to Magic Kingdom after the water park if it fits. If this was my trip, I would skip the water park and concentrate on the other parks.
With the Water Park option and more, you will receive four extras to use. They will expire 14 days after you activate the pass unless you add a no expiration to it.
Wishing you a magical vacation!
Beth