The best advice I can give you first off is to go to a pet store or a book store and find The Corn Snake Manual by Kathy Love.
This is the best book out there about the care, husbandry, and every other thing about corn snakes you could ever wish to know. Or you can purchase a copy from her website:
Cornsnake Manual at cornutopia.com
Its well worth the small amount and answers just about every question you could think to ask.
To answer your questions real quick:
1. How big do they get?
The majority of corns attain a length between 4-5 ft. Some may be larger and some may be smaller. But thats a good rule of thumb to go by.
2. How docile are they?
Most corns are extremely docile and easy to handle. Some may be nippy closer to when they're shedding and can't see that well, or when they smell food and you reach in and startle them. I've only been bit a couple of times by my adults and those instances were my own fault. Younger snakes tend to be a bit nippier, but I find cat scratches to hurt more and to do more damage. But if you treat them with gentleness and respect, you'll be paid that back.
3. Are there any special needs?
I assume you're refering to humidity, enclosures, etc. Corns do very well in a typical household tempreture and humidity gradient. If you live in a dry climate, then a moist hide is recommended to better facilitate shedding. They don't require any elaborate setups that is unless you can lavish the cost and space for one. I keep mine in relatively simple enclosures due to my own monetary and spacial limitations. A simple Rubbermaid container with locking lid, holes drilled/melted in the sides, a substrate of aspen shavings or paper towels, water bowl and hide does quite well. Again, the manual will help moreso on this.
4. Where can you find more information?
The Corn Snake Manual is the Bible for corn snakes. It's a good read for me, even after a few years owning corn snakes. I still consult it every once in a while. This forum is a vast library of information. Everyone here is invaluable, as is the search function on this site. If you have a particular question in mind, click search and input your query and voila, chances are its been touched on before.
5. Where can you find reputable breeders?
Well that all boils down to taste, how much money you want to spend, and location at times. Rich himself sells thousands of corns a year, as does Kathy Love and Don Soderberg. Those are who I consider the "Corn Snake Trinity". There are other smaller breeders who sell just as good a quality and sometimes for less. Each of us like to focus on one thing or another. Just search around until you find what you want and ask. The only stupid question is the one that was never asked. =)
Hope that helps a little bit, but I would definately recommend the manual first off before purchasing a snake. Best to be familiar with the territory and have everything prepared in advance before taking on the responsibility of an animal.
If you have any more questions, feel free to contact me or post it. =)