The living area over the barn is a cool idea but like Harley Heaven mentioned, the only drawback I can see is pest control. Our horses are not really close to the house and the flies are a real nuisance. Every time you open the door 3 or 4 get in.
In our county there is no planning and zoning so there are alot of small acreages with way too many animals on them. We know of people with 7 or 8 horses on 3-4 acre properties, which means it's more like 2-3 acres if you allow for the house and outbuildings. IMO that's just too many animals in a small place. They have no pasture and the horses are in dirt and mud all the time. This year the mud has been awful because we've gotten enormous amounts of rain so far. And the flies, ticks and other pests are horrible too because of the wetness. Not to mention the hay bills they have because they have to feed alot of hay year round.