Both races start at 6:05 on the 4 lane road to the east of the EPCOT parking lot (wheelchairs go off at 6).
They go through EPCOT, up the Main Drive, through the TTC, and enter the MK to the right, by the CR. They exit the MK by Splash Mountain, and run behind the MK, up to the GF and the Poly. The 1/2 finishes at the Poly, the full goes on to Coronado Springs, the Animal Kingdom, the World of Sports, MGM, by the Boardwalk, through EPCOT, then finishes in the EPCOT parking lot.
Runners and walkers must keep a 16 minute per mile pace or the broom truck will scoop them up, so given the start time, the last participant will exit the MK by 9 am (by the way, running up main street in the MK is totally righteous!).
So the MK isn't impacted by the race, but the Animal Kingdom, MGM, and EPCOT are. Runners will be going through them during the morning, but it isn't a problem.
The roads around EPCOT are unbelievable between 5 and 6 am, but if you have any sense you'll not be up then. I wouldn't be if I wasn't running.
The race doesn't impact park attendance much, except for all the visibly limping people you'll see Sunday afternoon.
So, enjoy the trip, the race won't have much impact on you at all.