Fiction books are not real. They are the creations of the author's imagination. The stories, characters, and settings are invented to entertain and engage readers.
There is no real difference. Both 'fiction book' and 'fictional book' refer to a book that contains stories, characters, and events that are made up by the author, not based on real facts.
Sure. 'The Book Thief' by Markus Zusak is great. It's set during World War II and tells the story from the perspective of Death. Another one is 'Wolf Hall' by Hilary Mantel, which is about Thomas Cromwell in the Tudor court.