Early entry starts at 8 am. The buses will begin running to EPCOT at 7am, the time you should be on will depend on your hotel but to see the rope drop and be at the front you should be on the bus by 7:30 at the latest.
Test Track, Soarin, Mission Space, Spaceship Earth are all open. If you want to do the big rides I find it to be worth it. You get an extra few hours of fewer people in the park. Although as the morning wears on it can get busier than other days. I like to hop out of the early park after lunch. If you plan on going to the park that day EMH is definately worth it, especially at busy times of the year.