In Florida climate won’t play much of a part, but it depends on the personality of your chickens, flock make-up (number, age, and sex), how you manage them, how hard you want to work, how much you enjoy drama with your chickens, whether you plan to integrate chickens later or let a broody raise chicks with the flock, and so many other things there cannot be a magic number that covers all bantams. If they are all the same age and all the same sex you probably don’t need a lot of room. You might follow the link in my signature for some things that can influence how much room you need.