On the issue of Avengers in each other's films - it's more questions like "why didn't anyone help out Tony in Iron Man 3" or "where the heck was Clint during Cap 2". Questions that are easily answered on a meta level (because that would be really expensive) but which require a certain amount of handwaving and/or suspension of disbelif to justify in-canon. They don't keep me up at night, but some people are really bothered by it. XD

Black Widow is not getting a solo film before 2019, and probably not at all. (Natasha and Bruce were my two favourites from the Avengers movie. The Phase 3 lineup was deliberately designed to spite me, clearly. ;) )