RE: your (1).

I think that Quirrelmort's aim was to turn Harry.

From Quirrel's point of view, Harry has shown incredible promise except for his pesky humanist streak. All Quirrelmort needs to do is to kill his faith in humanity off and he's ripe for the job of future Dark Lord. What better way to accomplish that than to have the wizarding world at large sentence the one person he believes to be wholly good (Hermione) to death? Dumbledore will refuse to help Harry destroy Azkaban and bust Hermione out, at which point Harry will lose all faith in him and his methods, and turn to Quirrel for help. Quirrel says, "Poor dear, didn't I tell you that people were basically evil if left to their own devices? They need a ruler to help them to be good. Let's break your chum out of Azkaban and take over the wizarding world for good measure as soon as we can, although I'm afraid that by the time we are in position to get her out and keep her out she'll probably be a vegetable..." So Harry and Quirrel sear Azkaban out of existence, free the crims (many of whom will now follow Harry into fire out of gratitude). Harry is left with a broken England and a broken Hermione and the only thing left for him is to rule with an iron utilitarian fist, Quirrelmort at his side.

And look how close it came to working! Harry's backup plan was to kill almost the entire sitting parliament of Wizarding Britain in cold blood! There's no coming back from that one. I don't think avoiding this plot inoculates him against similar attacks, either - if anything he's in a weaker position now and is therefore more vulnerable to being forced into the kind of irredeemable, desperation-induced act that he won't be able to put back in the box.