Guineas need quite a bit of space and an area to fly if penned all the time.
I free-range mine all day from the time they are about 3 months old, but pen them up with the chickens at night. If free-ranged, they really don't need much space, just a place to roost.
They lay quite a few eggs during the summer through August/September, but are VERY adept at hiding their nests. If you do find their nest, and they catch you or you take all of the eggs, they will start laying somewhere else, and the search begins again. Some people have encouraged them to lay in the coop, but I have not been able to convince them. The eggs are good eating though!
I have never had them successfully hatch their own keets. I hatched some under a broody hen once, and once in an incubator. They are very susceptible to predators while sitting on an unprotected nest (this is the only time I have lost them), and many keets do not survive long-term if left with mom.
