Poe makes Fortunado a character that most readers will definitely feel bad for by the end of the tale. He uses specific techniques to make him seem like a bit of a harmless fellow that certainly doesn't deserve the horrid fate the befalls him. First of all, Poe is not specific about the exact "injuries" and "insults" that Fortunado supposedly enacts upon Montresor. Because we do not have specific information, we can't really put a finger on Fortunado's villian status--it seems less real to us, and we don't feel like he is that bad of a guy as a result. If Poe had said instead that Fortunado had murdered Montresor's wife, for instance, we would have definitely NOT sympathized with Fortunado. But, all we get is that he had insulted Montresor. It sounds perfectly harmless, and we think to ourselves, "So? I get insulted all the time! Get over it Montresor!" By being vague about Fortunado's supposedly dastardly deeds, we sympathize with his end more.
Another way that Poe helps us to sympathize with Fortunado is by making him appear like a foolish but harmless man. Of all of the costumes Poe could have put him in, he chose a jester's outfit, complete with a jingling hat. This is a pretty funny image, to think of a grown man jingling around in a court jester costume. That lessens Fortunado's ominous character, and makes him seem like a jolly and harmless fellow. Then, Poe makes him drunk and rather amiable--he is willing to help Montresor, very friendly to him, and rather gullible as he is led about the tombs. That makes him even more sympathetic in our eyes.
So, by being vague about Fortunado's bad traits, and making him appear comic and harmless, friendly and gullible, Poe definitely paints Fortunado in a light that makes his vicious end one that we definitely feel he can't deserve. For your other questions, try submitting them one at a time as I'm only encouraged to answer one. I hope that those thoughts helped; good luck!