Hey, how many is to many, well it depends on how many eggs you would like to receive. the run and house also determines how many is suitable.a house that states that it can fit for example 10 large hens in such as ex bettery chickens i would recomend only putting about 5-7 birds in. this way they are not too cramped, and with more space and less birds they are likly to stay cleaner for longer, thus preventing risk of disease such as micoplasma which is common. Birds such as ex battery birds are about 18 mounths old and have an average life expectancy of about 2 years if not dispatched in other ways, syaing this some may live less and some from experience can live up to 5.it depends on each individual bird. however the ex battery bird is also normally weaker and more prone to other birds espeically when they have been kept inside all there lives.these birds firstly are bred for commercial use and are not developed to withstand diease. however they are vaccinated at hatch and ket inside from then on. so you find that if exposed to outdoor conditions they can pick up disease very easily and the diseases naturally picked up by others in which there body gets rid of themselves these birds are not able to do so. i would recommend buying exbattery birds befor ethey are too old to improve survival rates once free ranging and the offical free-range standard is having 1 square meter of room to 6 large hens however this is just stupid so just make sure you have room so that the chickens are happy.