If you have your heart set on MK (and I don't blame you!), as soon as you get in, ride the railroad to Frontierland and grab a fast pass for either Big Thunder or Splash Mountain, they may be for way later in the day by then! Since you'll just be arriving, wait in line for one of these rides if you can. We don't mind waiting sometimes at the beginning of a day (and it will be lunch time, so the line might not be as long). Then enjoy as much of the park as you can.
I know you said you were going to have a big early lunch, but since you are planning on staying until 11:00, why don't you ride the monorail to, say, the Kona Cafe for dinner. The monorail ride and the nice relaxing dinner will give you the energy to stay all night!
Have fun!