Found this lady. What breed (mix?) might she be?

[Park-hen]

Here are the generally accepted space recommendations for full-sized chickens:

-Coop: 4sqft/bird
-Run: 10sqft/bird
-Roost: 1ft/bird

Your setup sounds a little tight, but acceptable for 3 if you can't do better and particularly if they can get out and free range some of the time.

This is what I had concluded after much reading, so I'm relieved to hear experienced chicken keepers agree with the plan.