I will give you the same advice I give to all first-timers: plan for 1 day in each park and leave your 5th day open. After you have been to each park you can decide where you'd like to return for the 5th day. Don't attempt park hopping and keep your expectations of how much you will be able to do realistic. There is always the second trip (or third, or fourth, or...)

As far as the water parks and Sea World go, I would recommend saving those for another trip. If you still really want to do them this time, consider staying for additional 2 days. But I don't think they are worth shortchanging your time at the 4 main Disney parks. Don't forget to plan downtime in the afternoons - going back to the resort isn't absolutely necessary, but if you do want to stay in the park, find a place to sit and relax with a Mickey Bar or popcorn for a while. Most of all, be flexible and have fun!