I had my own private (no boarders) farm for 20 of my 37 years of horse ownership. During the other 17 years, I boarded at two places when I was kid (teenager), two places as a young adult, and three places just over the past 6 years since selling my farm.
As a kid, I was aware of flaws in the barns where we boarded, but we just made it work. Once having my own place, it was hard to go back to letting someone else call the shots regarding my horse’s nutrition and management. One barn was just a bad fit altogether because the BO was unreliable and very controlling at the same time. I went out of my way to make sure I wasn’t stepping on any toes, and the result was an unhappy horse and unhappy me. The second barn was better, but there were still some minor nitpicks (not enough bedding in stalls, no shelters in turnout).
When I moved to my current barn (and the best place ever), the facility wasn’t as “fancy” (though it’s getting upgraded all the time, even a covered arena being discussed), but the farm owner has the money and equipment and manpower to keep the facility safe, clean, and functional. The BM is a retired fellow who grew up at the farm, his father started it…the place has been there about 70 years…and he’s horse savvy but not a know-it-all by any means. He oversees the day-to-day and makes sure to relay to the BO anything that needs doing that he can’t handle himself.
One of the things he explained to me when I went to visit before making the move was that they were self-care. They would not provide hay, feed, or shavings. That was up to the individual owners to arrange and provide. The farm provided everyone ample storage for their feed and hay and tack, and for an extra fee, it could be arranged for the BM to actually give the feed. He explained that this was the only way to keep everyone happy because different horses have different needs and their owners want different things for them, so the barn was never going to be able to provide the “right hay” or "right feed’ or at the “right amounts” to suit everyone. And if people wanted more hay or a different type of quality of hay, that meant the price in board had to go up to cover the increase. And people don’t like that.
It works out wonderfully. For one, the barn is full of people who are knowledgeable about horses. No kids, all adults who are committed to making sure their horses are well cared for. We have everything from just backyard types to high-level dressage riders, and everyone gets along and helps each other out, etc.
I don’t know how many acres the farm has, but it’s large enough for 18 horses to live there and it doesn’t feel crowded at all. Many have individual turnout and I think the largest number of horses in one pasture is three. The place stays filled to capacity and people have to be turned away who ask about boarding. One horse just left, freeing up a two-horse pasture and shelter, and there are already two horses coming to fill that spot. We have cleared trails through the woods, open fields for riding, and our small ring is rumored to be getting enlarged and covered (we have a very generous boarder with the resources to help fund this and a BO with resources to actually get it built).
I will never be in the position to own a farm or offer boarding again, but if I found myself in your shoes, OP, I’d do just like this place does. You basically rent space for horse, tack, and feed/hay. The facility is kept very tidy (mowed, manure hauled away, pastures dragged, sand/dirt/gravel added where needed, arena and driveways maintained, etc.) Horses have eyes on them nearly all the time because the BO and BM live within sight of the place and the BM talks about watching through binoculars. If he sees a vehicle he doesn’t recognize or a horse behaving oddly, he’s in his golf cart and zooming down there immediately.
I can honestly say, it’s better than having my own place. I get to care for my horse exactly how I want. Even if I had to get the BM to feed (as I have when on vacation), he makes sure I show him exactly what to do. He feeds for the two upper level dressage riders at the barn, who are very particular, and they love him to pieces for how attentive he is to their horses’ special needs (one of them is PPID and requires medication, special diet, etc.)
I’d probably have a base level of board where I provide the bedding and clean the stalls (because some people aren’t going to do this to your standards), and then the owner can decide how much or little they want on top of that. They can provide their own feed and hay and do all of the feeding themselves. They can provide feed and hay that I feed. Or they can use the feed and hay that I provide and feed to their horse (I’d do a ration balancer and Timothy hay since those agree with most horse’s systems and meet their nutritional needs). Board cost would depend on which option they choose.
Sorry for the novel! Good luck with your endeavor!