Is there any issue to address or call a person (a gentleman, of course) with man? I think the word man has a strange meaning. Which is the best way to address? Is hello enough?
"Man" is used in informal contexts. If you are talking to a friend or a new acquaintance you could address them as "man," but it is not fitting for a formal/professional environment.
To address a "man" formally, one would say, "sir."
But "man" is okay for informal speech.