We do not know what happened that night for sure. You are basing everything you say on what GZ said. That is just his story. We do not know with 100% surety what really happen. TM hadwalk home in the rain. He nocar. He was staying with someone there, so he had a right to be there. GZ did not even know what street he was on. He surely would not everyone who lived there.
and....?
Traydown attacked Z. Period. It is all that is really needed.
Perhaps, but the other evidence corroborates GZ's account in virtually every detail we do know. GZ walked the detective through his "story" the next day. (Have you seen it - it is on YouTube.) GZ could not have possibly known at that time whether any "lie" in his "story" would hold up under scrutiny -- any window in that densely populated area might have held someone watching. He would have been exceedingly foolish to lie. Logically, then, since his account was truthful in the details we do know, it is almost certainly truthful in the rest, as best he could remember it. (Given the trauma of the incident, I am amazed he recalled as much as accurately as he did.)
The wounds on TM are the gunshot wound. The wounds on GZ are a smashed nose and cuts & scraps on his head. Could GZ’s wounds have happened after TM suffered his gun shot wound? Extremely unlikely. If TM had other than the gunshot wound (or scraped knuckles) then there would be room for speculation, but there are no such wounds. TM assaulted GZ. The physical evidence, the eye witness, all support this conclusion. There is no evidence otherwise.
None of that is in any way relevant. If Trayvon Martin initiated the violence, then the shooting was legally and morally justified. I have mixed feelings every time a thug dies attacking an innocent person - joy that the world is just a little safer for the innocent and sorrow that yet another parent did a terrible job in their most important role and raised a thug. Trayvon having a right to be there does not give him a right to throw the first punch, and neither does thinking (correctly) that he was being watched four minutes earlier.