Hey, it's great to have discussions - I'm sorry you were disappointed with the movie, but if we all liked the same things be a boring world wouldn't it?
Going back to point 16 - I think Khan really had no plan at all to keep any bargain with Kirk, he was simply going along with my "oh, woe is me" sob story until it was time to act. I suspect his superior intellect allowed him to realise he hadn't completely swayed Kirk to his side, so he was ready for Kirk's move.
The fact that, thanks to Admiral Marcus, Khan was
actually the aggrieved party helped his story along, but as to his turning at the end, I think that Khan really couldn't be anything else. He was conditioned during the Eugenics War, whether by his own desires or by design, to rule.
Khan in this movie is one of the best villains in Trek as he isn't a maniacal madman, he is at all points, up until he believes his comrades have actually been killed, in complete and total control. His manipulation of Kirk from the moment they have their discussion in the brig is testimony to this. And this harks back to his appearance in Space Seed, rather than TWOK when his brilliance is clouded by the losses he suffered over the years and his rage and thirst for vengeance.