When I go looking to place a cache, I load all the caches in the area into my GPS, where I want to put a cache, that way when I find a spot I'll check my GPS to see how close to any other cache it might be. I try to be .11 away just for a little buffer with GPS bounce. If your in a rural area, you don't need caches that close anyway. Puzzle caches are a different problem. If your in a more rural area, with not many caches, your most likely ok.
I don't use the geocaching map as I don't think those circles are not necessarily accurate. If you have a cache that you will have to spend a large amount of time to set up or construct, make up the cache page and then send a reviewer note explaining why your checking for availability. Once you get the clear sign go a head and place the cache and finalize the cache page and submit it. This kind of request from a reviewer tends to go to the bottom of the pile for caches that are ready so there response time might be a bit longer, depending on how busy there are.
As far as the distance thing goes, the reviewer in my area will ask me how I plan on maintaining the cache. If you can't give a good explanation on this they may reject it on that alone.