It always worries me when people ask about "maximum capacity".
That is never a good question to ask w/r/t pets or livestock, IMHO. (Not for the animals' sake, anyhow).
Consider asking, rather, "how few can I be content with, so that they can have the best living conditions possible?". Because more room really IS better.
Having tried 4 sq ft (indoors, with additional run) per chicken AND 15 sq ft (indoors, with additional run) per chicken, I would never ever go back to 4 sq ft because they really do act QUITE A LOT different with the greater amount of space. Also management is a lot easier, and problems fewer.
JMHO, good luck, have fun,
Pat