Personally, I’m kind of hoping they deafen him (as I’m sure you know they did in the comics at some point). I’m biased, though, because I have a hard-of-hearing daughter.
Actually, Marvel likes to occasionally bring up Hawkeye as a deaf (or at least hard-of-hearing) superhero, but his wikipedia page claims this was “cured” a while ago. In my dream world they would drop the whole “got too close to a sonic arrow thing” and the movie version would just be like “Oh, yeah, I have hearing aids” like it’s no big thing.
I suppose as a move scene it needs a payoff, so maybe he thwarts some villains mind-control attempt by turning off his ability to hear them, or something. (Although depending how it’s done that could be pretty cheesy, I guess.)
Correct, it happened within a single issue. However, she sought him out as a scientist first, and then he revealed his secret identity and gave her powers. No reason that she can’t have sought him out as a scientist in the movie universe, and hook up with him as such and not yet be a super-hero when he creates Ultron.