I know this post is a little old but I just saw it... We ranch from 3 to 15. We bring in horses that people don't want or can't any longer feed. My wife and I train or retrain them and resell them. We really like to train so we usually have a couple 2 year olds that hang around for a long time until they are finnished.
I'm curious too. How many acres per horse and how many acres per 1 head of cattle? I get conflicting info so would be happy to hear your ideas.
Here in Colorado you can usually keep 1 per 5 or 10 acres if you feed in the winter. We have 160 acres. We try not to keep more than 5 over the winter. Horses graze twice as much as cattle. We graze ours together.