I think I can answer 2 of your questions to Uncle Dave. By "single note melody", he means just playing a single note with the right hand. Usually, this might be the vocal line. Uncle Dave plays chords and harmony notes with his right hand.
By "signature line", I think Dave means a certain passage, bar or melody that is integral to a particular song. In other words, everyone would immediately recognize the song when you played that part. I can't think of a good example.
O.k.... never mind.... I'll just let Uncle Dave explain for himself...

Tom