This is a great thread! I am curious whether OP ended up on small acreage and what your experience has been.
Though my comments are late to the party, my view is that a lot depends on the layout of the property and the horses on it. I recently added a 3rd horse on our 5.5 acres, a property not originally designed for horses. On the plus side, it’s a mildly sloped property with spectacular oaks and conifers that has been nicely graded, it has great curb appeal to non-horse people, storm water moves through it fairly well, the perimeter is completely fenced, and we can ride to the community arena and trails in minutes. On the minus side, the house and gardens use nearly 2 acres and a lot of irrigation, the largest area suitable for contiguous paddocks is only 1 1/2 acres, the paddock gates are about 300 ft away from the barn and cannot be seen from the stalls, and the clay-heavy soil drains poorly.
The horses live outside 24/7 7+ months of the year, and more than half time the rest of the year. It was the 3rd horse that really tipped the balance away from the current set-up being workable in terms of paddock traffic, manure, and turnout and feeding efficiency. Our half-blind Andalusian mare cannot be housed with the geldings that inevitably try to to herd her or chase her off her food, and our retired WelshxQH needs to have his spring grazing restricted. While I could add a sacrifice paddock closer to the barn, it would cost a lot to grade, cross fence and foot an adequately sized area. I am now thinking of adding galvanized panel paddocks off my (converted garage) shed row stall fronts that could be removed should a future owner wants to use the building for another purpose. The area is already graded and has a crushed rock surface. Each horse would have a little under 500 SF in this configuration, including the stall space. Not ideal, but stall paddocks could work if used strategically AND I also sub-divide the existing paddocks and do a bit of rotation. I will also likely add a Newer Spreader to my farm equipment to deal with some of the manure, rather than picking up and composting 100%. If I had it do do over again, I would still have chosen a small acreage property, but one with a run-in barn and more acreage devoted to horse use.