No way is that enough land for 24 horses. As
said, you'd have to build a bunch of tiny paddocks. And then, because the horses spend so much time in them, you'd have to do something about the mud that's going to form after they eat all the grass and it rains in the bare dirt. You could lay down gravel or sand, which would be expensive, and then every few years it will start to sink back into the ground and you'll have to lay down more.
Yes, you will have to build arenas, an indoor and outdoor. Indoor arenas are crazy expensive to build. And that will most likely cut down on your pasture space.
If you wanted to have that many horses, and had them out eight hours a day, that's three times a day you'd have to move them in and out. Plus all the time you spend cleaning their stables. As a comparison, a place near where I live has 50 stalls and 23 acres, and it feels super crowded. They give their horses about two hours of turnout a day, and there is NO grass out there, just dirt lots. Also they have at least three employees there at all times to move the horses, feed, clean up after them, fix things that the horses break, etc. So that's another big expense.
And yes, you will have to feed 100% hay, year round. Ideally you would figure out how much you need for the year, then buy it in summer / fall when it's harvested. Do you have a place to store that much hay? For year round feeding, a rough guess would be maybe one - two tons of hay per horse. You can buy it as you go, but then expect to pay about twice as much.
With all these expenses, you'd have to charge a lot. If I were paying a lot, I'd expect a lot. Not just the indoor and outdoor arena, but a private tack storage area, nice washrack with hot and cold water, nice restroom facilities, etc. So there's more money you'd have to invest. And I can't speak for others, but me personally, if I'm paying a lot for boarding, I want to see lush green pastures.
Running a horse facility when you don't have a lot of experience with horses is absolutely a recipe for disaster. Most of the horse boarding places I know about barely break even. I would strongly advise against it.