One of the barns I boarded at in San Diego (San Marcos to be exact) back in the 90s had over 80 horses on 8-9 acres. Nearly all were stalled. We had a big jumping arena, and smaller schooling arena with jumps, and big turnout round pen, and two full size regulation Dressage arenas. You could pay for 1-2 hours of turnout in the round pen (was really a big oval), but most horses were just stalled 24/7. They were fed hay three times a day, feed twice a day if needed) and their stalls were cleaned twice daily. Lesson horses were in one of two "pastures" which were just big dry lots, probably about 1/4 to 1/3 acre each with 6-8 horses in each one. There was a BIG boarders barn that held something like 50 horses. There was a long "mare-motel" outside stalls that were 12x24'. There were uncovered 12x16 "stalls" and two rows of 12x24' outdoor pens that had three sided shelters at the back (about 12x8' shelters). There was also a small "lesson barn" that had 4 stalls and a big office/tack room.
The place was kept very clean by a fleet of hispanic workers that lived on the property. Hay came in regularly by the semi-load as did shavings. Manure was picked up in big dumpsters twice a week.
So, lots of horses on small property can be done, but it's always more expensive and a lot more work.