Concerning the hacksaw and hand, he probably did cut his hand off with the hacksaw because of how little time he had. May have given the cuffs/pipe a shot, but he couldn't even reach the hacksaw at the end of the intro, and the zombies appeared to be bending the door just enough to be able to make it through (almost).
Car alarm back to camp, stupid, but meh, he just drove through a city full of zombies on an adrenaline high, straight thinking could go to hell.
Apartment store. Ya, i woulda thought they would at elast try to barricade the door. The windows were glass though, so it wouldn't have made much of a difference. Those display cases weren't going anywhere.
Now if we want to nit-pick, I'd like to ask why no one has commandeered a gun store yet. With so many weapons available, you'd think someone would just take over a store and start shooting.