How many sons does God have?
evidently, more than one.
the bible doesn't give us a good answer on this one. traditionally, these are seen as angels, although "demi-gods" or "other gods" might also be appropriate. there are also a few figurative usages, applying the title to kings (thus, jesus, as the messiah is a king in the bayit-david. supposedly). adam is also refered to once (in the nt) as the son of god.
"son of man" is also used figuratively as a contrast, meaning "lowly mortal" (see ezekiel) and this "son of god" could simply mean "immortal." it certainly implies it.