How much room depends on whether you have little primitives or huge mules. I would say, to get the best from them, five little ones or three big ones to the acre.
Do you mean to breed them? If lambs are born in April they will fatten on good grass and go away in October/November. If you buy in weaned lambs in, say August, they will be ready to go without any supplementary feed at about the same time.
The only extras they will need is a digestive biscuit a day to keep them used to human contact. Not only does this make them unafraid when they go to slaughter but it keeps them close so that you can keep a good eye on them.
Smiley bucket needs a good old slap