How many free range chicken per coop size?

They may free range but they still have to sleep in there at night so you'll have to make sure you have enough roost space. Fights over roost space can cause a lot of stress if there's not room for lower ranking birds to move away from higher ranking or aggressive birds. I'm just really not a fan of tight spaces for chickens at all. Chickens also like to go inside when the weather is bad. I live in central CA and the weather here is pretty temperate but when it's windy/raining during the day my birds go in and enjoy hanging out in their coop until the weather passes. In my experience it's just always been far easier to prevent the problems brought on by overcrowding then to try to solve them later. But other people will say it works out for them. Guess all you can do is decide if you want to give it a shot.

 

I have Bantams & live in Texas also. My hens semi-free-range. They have a fenced-in yard about 25'x50' and their coop is only 4'x4'x4.5'. I have 16' of roosting space, although 4 only use the top bar and 2 of the Silkies stay on the floor in the litter.

I would be comfortable adding 2-4 more Bantams to this arrangement but I'm happy with the six.

And I might have "stupid" chickens but I have NEVER had them go inside the coop even when the chicken yard is flooding. They will try to squish themselves UNDER the coop and then become ducks when it floods.