I can't tell you what is recommended, but I can tell you we have 40+ goats and sheep on 5 acres. You set up paddocks and rotate! We are trying to expand right now and add 20 to 30 acres, but until that happens we are setting up paddocks to rotate everyone through the grasses and browse.
We grain, we mineral and we buy hay in the winter. That is the only draw back to the way we have the farm set up. We can't cut our hay 'cause the animals eat it. I think that 5 sheep per acre would be good, or maybe 4.