I use 5 johnny houses currently. problem comes when you have to service with water in the frozen months, because of the remote locations. It becomes tedious. As far as placement, you don't need that much room. About every 10 acres will suffice. Yes birds will migrate between houses, I had some Tennessee Reds a few years ago, released into one house. Within a month and a half, there were some appearing in all 5 I use, some a good mile away. Two spent the winter at a neighbors bird feeder, 1/2 mile down the road, came back in February after a 2 month vacation. I can approximate a pretty good immitation of wild bird shooting from my released birds. I got the idea from southern quail plantations, that's what they do, in this era of low populations.