^Everyone, whether it be Itachi, Minato, or whoever had doubts about Obito being Madara. But people just went with it, because they didn't know who else it could be and immortals were known to exist, like Kakazu who survived since Madara's/Hashirama's era. So it wasn't a stretch for them, though no one really (at least Itachi and Minato didn't) believed for 100% that Obito was Maddy. Both even died with their suspicions of him. TRUE STORY.
^Yeah. It happens when you go on a quest for revenge and give up everything, when you don't even know the truth and give up those 8 years of your loving brother in your mind for something that happened in one night, and don't think it's suspicious but act upon your emotions entirely and throw common sense out the window and don't try to find out if there's something more to the story.
Poor Sasuke. Don't really blame him for the taking revenge part though. Itachi knew that he'd do it and wanted him to, because he knew that it would benefit his little nii-san in the end. But everything that occurs after Itachi's death can be considered Sasuke's fault.
No, just joking. He is well-drawn though. He looks quite boss if I do say so myself. U_U
It's obviously a hyperbole. He's not sweating because he's an edo though. Amaterasu is hotter than regular fire, considering that Itachi's katon didn't make the stalactites retract in the cave with DSM Kabuto, whereas Amaterasu was so hot that it did and Kabuto even made a comment about the heat radiating from it.
^I'll have to go with Itachi on this, even though he's a fictional work. I learn more lessons from him than I would from a pop star who's music I don't like. Though, kudos to Justin if that's what he enjoys doing in life and makes a good-living from it.