Because they may spend time confined to the coop/run area you need to allow as much space as possible in that area -- a good minimum is to plan at least 4 square feet in the coop (not including space occupied by feed, water, etc) and 10 square feet outside. That being said, the more room you give them, the less likely you will have issues resulting from them feeling overcrowded so more is always better. Additionally, if there is any chance (ie you are not restricted by regulation) that you may want to increase your flock (hint, except when legally unable to do so it nearly always happens) it is, again, best to build bigger than you think you need now vs. trying to remodel later to make more room in the coop to allow for more birds.
As to keeping the birds home -- clipping one wing's flight feathers can be very helpful in preventing them from going over the fence. In addition to the potential of the neighbor complaining, they are also at risk of injury or predation if they are outside the protective boundaries of your yard.