A rescue!! We don't have enough of those unfortunatly... you can combine the two.. rescue horses and turn them into school horses and sell them to good homes!!
Sorry I kind of jumped around, having a lesson facility, if you live where winters get bad, have a heating indoor arena. You can then ride all year round
A rescue facility is good but you might end up with more horses in then you are finding new homes. A lesson/boarding facility is also good but just so you know, owning your own business can be hard. In the horse world especially
Hope I am some help