I found this good resource on feeding chickens. It answers several questions I've had and have seen asked: How much do they eat and what types of feed should I give them? Do I need to feed them grit and how much? How long should I wait after feeding medicated feed to butcher or eat their eggs?
http://animalscience.ucdavis.edu/avian/feedingchickens.pdf
http://animalscience.ucdavis.edu/avian/feedingchickens.pdf