I answered this as 'You are a unique guy' which was wrong. Is אדם just person, not male in paricular?
It can be used for a woman too, but in this case "אתה" is definitely a guy. So it probably should be accepted.
Not really. In plural, though, you only use בני אדם. I think the species in biology is called האדם, rather than בן האדם (but only in singular).