Bucky was indeed responsible for Howard Stark's death in the comic universe. But keep in mind that comic storylines can sometimes be complex and subject to different retellings and revisions over time.
Howard Stark's death in the comics was a result of a conspiracy. He was targeted by powerful foes who saw him as a threat to their plans.
Yes, the Winter Soldier did kill Howard Stark in the comics.
Yes, Bucky did kill Tony Stark's parents in the comics.
Iron Man and Howard Stark would likely start with a bit of shock. Howard might be amazed at the technology Tony has created, and Tony would be in awe of seeing his father alive (if it's that kind of scenario). They'd probably exchange some witty remarks, with Howard being a bit more old - fashioned in his speech. Then they'd start discussing technology, with Howard offering some of his classic insights and Tony showing off his modern advancements.
The portrayal of abuse involving Tony Stark and Howard in fanfiction is quite diverse. Some stories might touch on it to add depth or drama, but not all do. It's really up to the imagination of the fanfic writers.
Pepper Potts can also be a great addition in some of these fanfictions. Even though she's mainly related to Tony, her presence can add a different dynamic. For example, if the fanfiction is about Tony dealing with Howard's legacy, Pepper can be the voice of reason, helping Tony see things more clearly. She can also interact with the memory or apparition of Howard in some creative ways, which makes for a great read.
Yes, Bucky is depicted as bi in some comic storylines.
Yes, Bucky was depicted as bi in some comic storylines.
Bucky was not presented as LGBT in the comics. The character's development centered around different plot elements rather than this particular aspect.