I would would aim at getting 8 or 10 young yearlings, letting them grow off during the summer. Then I would sell the ones I didn't favor as much. If you saw where your grass wasn't keeping up you could sell more. You just don't want to have to feed and hay all the time. I've seen 5 head keep good weight on 15 acres though. Plenty of variables, just try it and see. You will know better than anyone else.