1) I like it, but I would also have been interested in seeing it in landscape format. He clearly seems to be looking out at something, the landscape format would have enhanced this feeling.
2) I like the composition of him, the walkway, and the sky, but I agree that it's too busy directly behind him.
3) I go back and forth, but overall I think I like the unorthodox beheading. Personally I might crop a bit more from the left, so that the guitar is evenly centered in the frame rather than having extra "dead" space to the left.
4&5) Solid, though I go back and forth on whether I like him looking out of the frame in #4 rather than looking into it.