Well, without more details, it's hard to say exactly who he is in the context of the ghost story. He could be the protagonist who experiences the ghostly events.
I'm not sure if there is a specific 'bang' related directly to a book by Barry Lyga in his stories. It could potentially be a very specific reference within one of his works that I'm not familiar with. You might want to check his official website or a detailed book review site for more information.
As far as I remember, in 'A Christmas Story' there was no character named Barry. The main characters were Ralphie, his family members like his mother, father, and his little brother. There were also the school bully and the Santa at the department store, but no Barry that I can think of.
Not necessarily. Barry might draw some inspiration from real life, but it's likely to have been embellished or fictionalized for dramatic effect. Many stories like this take liberties to make them more engaging.
It could be the Time Wraiths. Since Barry is taking on the identity of Savitar, who was a time - aberration, the Time Wraiths might come after him. They would view him as a threat to the proper flow of time and try to eliminate him, making them the main antagonists in this fanfiction scenario.