8 x 10 would probably be ideal for their indoor needs, and each 4 or 5 hens can share a nest box. You can use buckets laid on their sides, but if they're just laid on the floor of the coop, the chickens tend to tread and poop in them, getting them dirty--thus making your eggs poopy. You're...
Actually, the recommended outdoor run space per chicken is 10 to 12 square feet, with 4 square square feet of indoor coop space recommended... so if you kept 10 or so hens, you'd probably have the fewest problems with parasites, aggression, cannibalism and so forth.
10 Rhode Island Reds will...