An excerpt from a university article on cottontails.
http://www.naturalresources.msstate....ail-rabbit.asp
"The species survives because they reproduce up to seven times per season.
For successful reproduction, the cottontails’ habitats must be in close proximity to one another. Eastern cottontail rabbits do not travel far and usually spend their lives in an area no larger than 10 acres. A small area with open fields for foraging and plenty of edge brush for nesting provide the most ideal habitat. Proper maintenance of these types of habitats allow eastern cottontail rabbits to thrive."
So this give you an idea of distance apart for the cottontails. Consider carrying capacity for your ground too. If you have lots of brush and grass the land could support lots.
The hares like fence lines with open fields nearby. Maybe put a pallet hotel or two along a fence line too.
Rabbit population cycles go on 9 to 10 year highs too so it may not increase rabbit populations for a year or three.