This is like saying "is that a question?" when someone is talking about something without making a clear point or asking a direct question. As a clause inside a larger sentence, you could use it in a number of ways, such as "are you asking me to do _" or "are you asking me out", etc.
Yes, I'd say that. Possibly I'd be more likely to say Menar du det som en fråga? 'do you mean it as a question' in real life, but there's nothing wrong with Är det en fråga? either.
I don't think it would be used in this context, but Är det en fråga om...means "is it a question of..." (facts, morals, the law, etc.).
In the sense, do people sometimes say that in Swedish, yes.
In the sense, is it an accepted translation on the other side of this sentence, no, because that would be You're asking me? in English.
That would be ifrågasätter.
Ifrågasätter du den mäktige Duos vilja? (not quite sure vilja is the best translation of will here though)
Just to have it correct in my head. I put do u have questions, but this would be 'har du frågar'?