The Large Horse Farm
If you're interested in breeding or training show horses or race horses you'll need a large parcel of land that has large dry, flat tracts. Room for roads, barns, pasture, training facilities, veterinary paddocks, quarantine stalls and things like hay, feed and bedding storage, storage for equipment necessary for daily activities, tack rooms and garages for tractors and horse transportation and areas to hold manure safely are critical. You'll need to have provisions made to get water to horses that are pastured and have proper sheds to allow them cover in case of inclement weather. Those are just a few things to keep in mind.
The Small Horse Farm
The small horse farm requires the same things, it's just the scale that changes. Just because a property has enough land to qualify as a horse property under Town regulations doesn't mean that it would actually work as a horse farm. If you've got a property with 5 acres, a large house set in the middle of it, a long driveway with an expansive lawn, you haven't left much of that land for your horses. If you try to house horses on an inappropriate property, they won't prosper and the property will be torn to shreds.