Within the limitations of your visit - you can definitely do this! I would go to MGM in the AM, at opening - get a Fastpass for one and ride the other (Rock N Roller Coaster & Tower of Terror. Then do the other must do rides on your list, and head over to Typhoon Lagoon around noon for the afternoon. I would hang at Typhoon Lagoon for the afternoon - then go back to MGM around 5 o 6 pm, get some dinner and see Fantasmic, as well as anything else you have time for.
I don't know if Typhoon Lagoon would be full by noon - we've only gone in wintertime, when only one water park is open, and it was not packed (too cold!). I do know that MGM is a partial day park for us - we still haven't seen everything we want to, even after 3 trips, but my youngest (6) has a built in button - as soon as she passes through the MGM gates - she wants to be back at the resort swimming! I don't know why - the atmosphere at this park just doesn't hold us there like MK or Epcot! We do enjoy the rides, and the shows - but in small doses!
Are you going on the Fairytale Package? If so, I probably wouldn't bother going to Universal for a day! I would save that for another trip. If not - have fun!! I would like to get to Universal someday to see Shrek - that's our family's favorite movie - but Disney has us hooked - once we get on property - we just can't seem to leave, even for a day!