The importance of the setting/staging within this play. How would the play be different if the setting/staging were changed?

I would say the physical set construction or backdrop of the "fence" where Troy sits is extremely important.  The opening scene where he is talking with his friend in his backyard helps to show the physical aspect of separation.  Notice that we see Troy not in his home, not interacting with his immediate environment, but physically separated from it.  I think that this is a reflection of his character as being divorced emotionally from his world.  Sometimes this was done because borders or partitions were put up to prevent him from doing so and at other times, it was his own creation.  The physical construction of division and partition helps to reinforce this emotional construct present in how Troy views himself and his world.