I understand those that feel they have been staged in the wrong corral but I feel they may be instilling undue worry in WDW running rookies.
If you are the 25,001th runner to cross the START LINE, that doesn't mean you have to worry about 25,000 runners in your way.
(Unless of course you are the Brazilian dude that usually wins.)
The reality is that you have so many runners doing their own thing, any time during the race may turn out to be an ideal window.
You have folks trying to PR, those that stop at every photo op, ride rides, drink beer, visit with family spectating, run/walking, etc.
Unless you leave at the front of corral A, (Spoiler alert*) you will literally have thousands of people in front of you the whole race!
The good news? They are spread over 26 miles!
I have started from C corral to the last corral and in between and haven't had a bad, or overcrowded run at any time.
I actually started next to dead last one year.
During the ice bowl of 2010, you could basically choose your corral since the volunteers were more concerned with hypothermia.
One advantage of a faster runner leaving a slower corral is the speed difference, especially in the first couple of miles.
If you have a large pack of runners and the ones in front of you are moving just slightly slower than your ideal pace, you have to make a decision.
"Should I pass or chill for a bit?" Whereas, if you are much faster you simply pass them.
One of the more interesting things is the way you tend to leap-frog runners and then they leap-frog you.
They stop for pics and you don't or you run/walk, it happens that you see many of the same folks for many miles.
The true bottlenecks are cone alley after MK and before Grand Floridian is the one I hate the most.
Second place belongs to the tiny sidewalk outside of AK. Groan!
These spots will likely be packed regardless of your corral.
As for the character stops, I believe they police themselves. If they are too crowded many people just run by.
For most runners there are one or two "must stops," otherwise get them next year.