I am not quite sure how they would get up high to a perch.
I might open up the lowest level too, since that would be easy for them to get to.
Here on BYC the standard answer to "how much space per chicken" is 4 square feet in the coop and 10 square feet in the run.
If your hens are sweet towards each other, you might be able to get by with less.
If it is too little space they will start pecking at each other.