The way I see it, they will build Sharon and Caps relationships over this film and the third film... There's no need to rush it... If u look what at how they handled Peggy and Tony's relationship, they built it from Iron Man 1 and Iron Man 2... They didn't just jump into the romance like we seen on Thor, it was a slow progression which culminated in them finally being a couple in Avengers.
Sharon will be meeting her "idol" in this film, it shouldn't be a straight jump into romance, he is still coming into terms with something things, he still needs to resolve the Peggy situation and maybe that doesn't even happen until the third film.
Falcon will fulfill a similar role to Bucky's in CATFA, and Cap will only probably learn about Winter Soldier being Bucky in the second act, and I don't think they will drag out how Cap comes to terms with that situation (how many problems can be explored in one film).
He will probably just want to do what ever is necessary to bring Bucky back to his senses.
As for as Black Widow goes I definitely think she will serve a purpose. In the comics Cap and Widow always worked well together, and in Avengers we see camaraderie between the two. Not to mention the obvious ties she has with Winter Soldier.
So if Cap is going to go after the Winter Soldier and his employees, why not take the one person that he respects, and has a whole lot more experience with these sort of people?
I think Widow's presence in the film will be totally warranted, and if Hawkeye is in the film, he will be a character that would be a bit more forced in, but will probably be Widow's confidant, and he will have some cool action scenes and much needed face time.
