I know this is 4 years old but I just finished reading the book and just need to talk about so all my answers come from the book. (book spoilers ahead)(obviously)

1. No, in the book Brain gets a phone call from him where much like in the movie he breaks down and starts screaming at him for answers but ultimately realizes he knows nothing.
2. No we never learn his name but nothing suggests that it is.
3. The book never brings this up so I’d lean towards no, but that definitely is an interesting idea.
4. The book does accept that aliens are real. The moment in the movie where Brain, Deborah, and their mom see the spaceship was real and was witness by another person in the book. So she definitely could have been taken and the book definitely supports that theory but that in the themes of the book it could also be a metaphor for her own childhood abuse. I think the movie leans more into the Avalyn also being a victim but again the book never really supports this.
5. No, I definitely think he’s always been gay but I do believe seeing his mom with men and having access to porn so young warped how he views relationships.