Well, let's see--Homer wrote his epics when? about 700-800 B.C.? They were sung, were they not? David wrote his psalms around 1000 B.C. and included musical directions in some of them. 500 years before that, Moses sang a song after escaping from the Egyptians, the lyrics are in the book of Exodus. The Epic of Gilgamesh predates that by several hundred years, I believe. Was it sung? These should qualify for your first two questions. As for the oldest non-professional/non-ceremonial song, find the age of the oldest professional/ceremonial song, post date it by ten minutes, and you're there. Human nature being what it is, I'm sure there was some wag around making a parody of it as soon as it left the lips of the originator.

I'll leave the forth question for Bruce O. and Frank I.T.S has answered the fifth.