Zimmerman has neither your size, nor your Chessies as an intimidation factor.
One thing that I haven't read anywhere is at what distance Zimmerman was following Trayvon. If he was staying half a block or so behind him, that should have given Trayvon plenty of space to be able to get home without incident if he had just made the sensible choice.
As far as your what if, if Trayvon thought that Zimmerman was a robber, well, then, it was very foolish of him to confront him when home and safety were only a few yards away.
My sympathies began to swing to Zimmerman about the time our friends Jesse and Al began attempting to color the event as a racist act, and continued to swell as the media kept publishing the photo of 10 or 12 year old Trayvon instead of one showing him as he actually was (17, 6'+, and, at least at times somewhat thuggy looking). Made me feel like they were hiding something and began to sound like a lynch mob. Then there was the fact that that group was claiming that the "white man" was profiling and stalking some little black kid and then, in the words of one congresswoman, "shot him down like a dog" which is demonstrably NOT what happened. to top it off, when it turned out that Zimmerman is in fact part Hispanic, they actually went so far as to refer to him as a "white" Hispanic (whatever the hell THAT is). Would be laughable if it weren't so blatant.
So, get rid of all the hyperbole, and what I think it comes down to is; Zimmerman was aware that there had been a series of break-ins in his neighborhood. Zimmerman saw someone acting in what he felt was a suspicious manner. Zimmerman called the police to report the activity and then decided to attempt to keep an eye on the person until police arrived. Zimmerman did NOT attempt to "apprehend" or in any other way molest Trayvon. Zimmerman did not go "hunting" for Trayvon with blood in his heart and gun drawn. Trayvon noticed Zimmerman watching and following him. Instead of proceeding to the safety of his father's house or calling the police to tell them that HE had seen someone behaving suspiciously, Trayvon decided to not only confront Zimmerman but to actually assault him. Trayvon then did attack Zimmerman, striking him in the face, knocking him to the ground and then beating his head on the concrete sidewalk. Zimmerman then pulled his legally carried firearm, discharging it ONE TIME which apparently cooled Trayvon's jets causing him to break off the attack and unfortunately resulting in Treyvon's death.
From what I have read, that seems a plausible scenario, and it would be my position that in that case, Trayvon's death, though unfortunate, was not a crime.