How much land, and how are your fences, and how many horses will be the limit.
Will you provide hay? What about water? Is there shelter, and how much?
Keep in mind that every time a different horses comes in, that there will be a battle as they readjust, and that means you have to have a place to separate them first.
And do you have a place to store tack or for people to ride?
I had been with the woman I had horses pastured with for right at 4 years. Safe place had been made for Kola, so he could stay out of sun, and off grass. Thought it would be fine. He had small area to go out in at night, when sun is down.
Woman's mom talked her into "training" a horse for 10 days. 10 lousy days. Horse got there, was put into Kola's secure spot, which meant he had to stay in stall, not good on his knee. So opened up another area for him to be able to at least move around in.
New horse came Thursday night. Other 6 horses got through 3 gates, (supposedly) and came after Kola, running him through cattle chute, and knocking huge gate off hinges too. He didn't have one area on him that wasn't bitten, cut, scratched, sore, marked up, or wasn't swollen, plus he had huge puncture wound where a bolt had gone into his point of shoulder.
I moved them ALL the next day. Kola was taken that day, Sunday to my vet, and stayed there 5 days. I went and got the others on Monday, and my round pen, and things. Still have to get hay and dog kennel but will. Just been too hot to try to get those.
But she lost board for 3 horses, due to a 10 day horse. Kola should not have lost his area, as I had been told it was made for his use.
That can make or break someone boarding with you.
Horses make me a better person.