How does Poe motivate the behavior of Montresor? Does the story provide any hints as to the "thousand injuries" he has suffered? Are any hints necessary?

There were no hints necessary, one would have to read the story plain and simple to see how Montresor was treated by Fortunato, how he was hurt within, mentally or emotionally injured. (the story provides some hints, just scan through and itll end up popping out at you, dont rely too much on the internet for answers)