When Snake approaches the Happy Kingdom amusement park on the hang glider (with the others) the sun is just coming up. Half an hour later (in the story), when Snake makes it off LA, it is dead of night.
A gun cannot simply be converted to fire blanks by swapping out a magazine of live rounds with one loaded with blanks; the gun will not cycle. It would require a military blank adapter (which would be very noticeable to Snake) or extensive modifications to the internal mechanisms that would make firing live rounds destroy the gun. Also, firing blanks from an unplugged barrel at such close range is still dangerous, and would cause serious harm or even death to his intended victims.
When the "contestant" before Plissken fails to score and is shot, the locations of the shooters and the direction of their shots guarantee that several of the shooters would end up shooting each other, and they didn't.
In several scenes the face of the stuntman is visible and clearly different from Kurt. When he climbs up a ledge of a building after the rest of the structure crashed down. And when he rides a motorcycle on the back wheel.