Do you really mean 8am-12pm (4 hours)? If that's all the time you have, you'll only get to "hit the high spots." If you're looking to do nearly everything and you actually have an entire day, check touring plans' "Ultimate Touring Plan" for the Magic Kingdom.
No matter how much time you have, the best strategy is always to arrive before park opening, hit the most popular things first (e.g., the Mountains, Peter Pan, Pooh, Jungle Cruise, Buzz), and/or get fastpasses for later. Then as the crowds begin to build, move on to the attractions that are less popular or for which lines build slowly. By mid-afternoon (and if you're not trying to do absolutely everything), you'll have covered most of the park and can relax and revisit your favorite attractions. Check the TImes Guide for that day to see what entertainment is available, and plan around any parades, etc. that you want to see. For dining, we've never had a bad experience and it depends on what kind of food you like. Visit the dining section of this site for menus for the restaurants in each park and browse through them. If you plan to eat at a non-standard time (e.g., before 11:30am or after 2pm for lunch, or before 5:30pm or after 8:00pm for dinner), you'll have better seating options and more prompt service.
Good luck - I'm sure it will be a fantastic day!