One of our best sources for this kind of information in the early medieval period is the Domesday Book, compiled by William I in 1088 to assess the value and taxable income of his kingdom. You can access a digitised version of it online at opendomesday.org.

As a case study, we'll look at Dorset, which is prime wool-farming country. The Anglo-Saxon royal vil at Wimborne Minster was a significant Anglo-Saxon settlement, with a population of 51.3 households (likely around 200 people), and the lord received £4 a year in rents. Many of the townspeople would have been involved in arable farming (there are three ploughjng teams) but there's also a record of 127 sheep and 30 goats. Wimborne's tax value is surprisingly low, given its stature, and this is likely because much of the land in and around the town was most likely owned by the minster church at St. Cuthburga's, which had been the family monastery of the Anglo-Saxon Cerdicing royal house, and thus exempt from taxation. That 127 sheep may well have been in one flock.

At neighbouring Charborough (population ~45), there are 105 sheep. There are 13 households at Charborough: 5 villagers, 4 smallholders and 4 slaves. Smallholders are likely only slightly more than self-sufficient, so it is likely that the flocks would belong to one of the 5 'villager' households. Given there are 3 ploughlands and a pig herd at Charborough, it seems likely that the 105 sheep constitute one flock.

Another prominent nearby town, Spetisbury, consists of 30 households, of which 10 hold land sufficiently extensive and productive to qualify as 'villagers'. There are 6 ploughlands (although 7 plough teams) at Spetisbury, as well as at least one pig farm and a small herd of cattle, and 166 sheep. Accounting for the number of villagers, this could be one large herd or two smaller herds of ~80 sheep. Either way, taking this small corner of Dorset into account, sheep farming was likely the preserve of only one or two households in a prosperous town or village, with flocks of approximately 80-120 sheep.