2560 square feet is plenty of room for the amount of chickens you want to raise. Generally, if hens don't have access to the outside, they should have at least 4 square feet of space each inside. Using that number, your 2560 square feet room could hold over 600 chickens. However, I wouldn't recommend that. Chickens that aren't overcrowded grow better, lay more productively, and are healthier and happier than birds that are crammed together.
I only have a few large fowl chickens, including the Columbian Wyandotte I mentioned; I have them for eggs and pets. I also raise bantam show chickens (White Wyandotte bantams and Dutch bantams). Currently, all of my birds are eating a 16% protein layer feed from a local feed store. In the past, though, I have also fed a gamebird grower feed with 22% protein. As long as you feed your birds quality, fresh feed that has at least 16% protein, they should do well.
