Yes. Whisky Galore is based on true events, although some artistic liberties might have been taken to make it more engaging and cinematic. But the core of the story is drawn from reality.
It's not a true story. The film is more of a creative imagination, although it might draw inspiration from some common situations or cultural elements, it's not based on actual events.
Obviously, Harry Potter himself is likely to be one of the main characters. He often gets involved in all sorts of magical happenings. Hermione and Ron might also be there, as they are Harry's closest friends and usually accompany him in adventures.
Well, one interesting plot could be the goblins forming an alliance with Hogwarts students against a new dark threat. They might use their skills in magic and their knowledge of ancient spells to help in the fight.