I'm going to give The Great Gatsby a try, though it turned out to be way harder than I thought!
1.) Initially I was going to go with the protagonist Nick leaving the Midwest and moving to New York, but this event doesn't seem to really get the gears of the plot turning - it initiates the story, and without it the plot couldn't be set in motion, but it's too bland and feels more like requisite backstory. I suspect the inciting incident is Nick becoming Jay Gatsby's neighbor - but I'm not too sure. The problem here, again, is that this doesn't exactly trigger the plot. I feel like the plot arc begins when it's established that Jay Gatsby wants to reunite with the married Daisy Buchanan, but this doesn't happen till we're well into the book.
2.) External conflict is another tough one, because Nick is a special kind of first-person narrator/main character; externally, he's almost peripheral to the plot, and acts as more of an observer or interpreter of events rather than a pivotal participant in them. The external conflict of the plot seems to be character vs. character (Gatsby vs. Tom, Daisy) but the external conflict of the story or main character arc seems to be character vs. society (Nick vs. the moral corruption of aristocratic society, embodied by almost everybody except Gatsby, who "turned out all right in the end"). If I had to choose one, I'd go with the latter.
Over the course of the story Nick changed (as he describes it) from a tolerant person who reserves judgments to quite the opposite - this might be character versus self, a conflict between who Nick used to be (or who he believed he was), and who he became (or who he really is).
3.) The tension in the first scene - the small dinner party at Tom & Daisy's mansion - is powerful. The night is constantly being interrupted by the ringing telephone with Tom's mistress on the other end. The tension is maintained by having the affair be an open secret - no one can talk about it openly, but the insistent phone shatters the illusion of Tom and Daisy's marriage over and over again. There's also a small hint that Daisy (and her friend Jordan) know Gatsby, Nick's new neighbor, somehow. The reader wonders how they're all connected, and what will become of this troubled marriage.