Safe shooting area depends on what your shooting. For buckshot or slugs, I assume your shooting at fixed target? I typically shoot into the side of a hill, with nothing behind it for at least a few hundred yards, and don't shoot buckshot/slugs into the air unless you absolutely know where the shot will fall.
On flat ground shooting flat, buckshot or slugs will typically hit the ground by about the 200 yard mark.
Birdshot fired in the air, such as shooting skeet, won't travel that far and has nothing left when it comes down. Only real risk for falling bird shot is getting it in your eyes. I go to a dove hunts each year, and in a field full of hunters your constantly getting rained on by bird shot and it's no big deal.
Standard shotguns are setup for right handed shooters, ejecting the shell out to the right. If you shoot a right handed shotgun left handed, the ejected shell will pass very close to your face, if not hit you. You can get both pump and semi-auto in left handed models, or double barrels in either side-by-side or over/under. Any of these should work for you, the double barrels are typically much more expensive.