The space is just about adequate but it will be bare in no time, so you might have to put down straw or bark and some "toys" to amuse them. Two runs would be better so that you can rest one. I would suggest you buy six hens and see how it goes. If you buy 12, which is the absolute maximum you can accommodate, in a couple of years you will have very few eggs and twelve elderly hens, unless you are prepared to cull them. Get six now and six next year, or 4, 4, and 4.