Andy Lee in his book Chicken Tractors talks about (if my memory is correct) raising 25 birds in a tractor. He says it's a bit crowded at the end, but it works fine.
I began my chicken adventures YEARS back based on his book. His advice has always served me well. In fact, my original tractor...
About 20 years ago I had an Americana who laid 2 pink eggs every single day and one or two days a week she laid a 3rd shell-less egg. At the time I had 4 hens, no roosters or any other birds. The other three laid aqua and green eggs so no confusing who laid what. It took a while to figure out...