D.D.
We did Orlando for 10 days Nov 08. We did Universal and Seaworld. We only did 1 day at Disney and did Magic Kingdom. It was rough and barely saw stuff since it was so busy. I would ask him where he wants to go and what he wants to ride/see/do. And go from there. My daughter loved Seaworld and since it would only be a day maybe you could do aquatica a second day. Same price and he would get to swim with Dolphins. Also my son was 7 and really liked Universal because they had the superheros. We are going again this year and only doing the Disney Parks.
Have fun!!! It doesnt really matter how much you see or do as long as you have fun and dont get stressed, he will have a great time.