We have nine acres ourselves, and rent an additional 12 or so from (non-smallholding) neighbours. At the moment we have about 15 - 20 breeding ewes, 6 goats, raise weaners (3 or 4) during the summer and just under 50 poultry (we rear our own replacement layers, so about 15 of them are young males destined for the coq au vin pot). I am trying to increase the numbers of ewes, but as I am the "only" fulltime farm worker here, I am at the limit of what I can look after. (also large p/tunnel, veg garden and 2 young children).
It really depends what you can afford (you can always rent out additional land that you cannot use in any particular year - we have had cattle co-grazing with our ewes/lambs this summer and it has been great), and how much time/money you have to look after it. Also depends on the quality of the land.
Also keep some money aside to buy machinery, repair buildings/fences etc, buy a trailer etc etc etc.