We are currently babysitting 2 hens that belong to a friend. We used to have quite a few (36 at one time which is too many) They are quite easy to look after and I would say that 2-4 is a good number to produce eggs for yourself and friends. The best place to get them is your local egg farm, battery or barn as they are just a plain brown hen and are bred to be egg laying machines, the rare and exotic ones don't produce the same.
Ask your local egg farm when they are next changing out their hens. They usually get them in at 6 months old and get rid of them at 18 months old after they are past their best. You can usually get them for free, or a couple of quid.
They are in a right state when they come from the farms with bald patches and the battery ones can't even walk but within couple of weeks of getting them home they are good as new and will still produce an egg a day for the next few years.
The hen ark in the pictures would be the right size for up to 4, Because they are not mine I only let them out supervised so they dont get killed by foxes or dogs or raptors, but I used to let my own out all the time as it means less wear on a particular bit of grass.