Off the back wall is most important since they are rear ported and move a lot of air. At least 12 inches, more if you play it loud. (mine are 24 inches off the back wall)
Off the side walls next. Off the walls and away from the corners because they can be boomy.
as to space between them I found 8 feet is better than 6 feet.
I have found that off the walls is more important than distance between them, but I have 16 feet to work with at my house.
Toe in, that's where you decide. You can adjust this several times to your liking. I never settle on one toe actually. It certainly depends on how far apart they are from each other, and how far back you sit. Klipsch still reccomends toe in facing the sweet spot where you sit. The triangle.
But I find that facing more forward with little toe in creates a bigger (more realistic) sound stage.
