1) Well, in my country it's appropriate for everyone. People of any age can play the joke.
2) They usually ask some fun questions or tell short stories with serious faces. People try to make others believe strange offers, ideas , tasks in any unexpected situations.
3) Yes, most of often it works. In particularly, if people prepared some jokes in advance.
4) Their faces become surprised firstly and after that they usually start laughing. Or just sincerely smiling. It always happens in friendly and warm atmosphere anyway, coz everyone understands it's just an April fool's day joke)