Nolan Price would not have been allowed to prosecute the defendant, as he was directly involved with the victims he would have to recuse himself on the grounds he could not maintain impartiality.
Two detectives would not be permitted to attempt to apprehend a suspect known to be armed and dangerous, alone with no backup. Standard NYPD procedure in this instance would be to have an ESU tactical team present when dealing with an armed suspect, they would take the lead on pursuing and arresting the suspect, as that is what they are very highly trained for.
Nolan clearly enters the City Hall train station, but he ends up at the Canal Street platform nearly a half mile away. That being said, Canal Street is in the heart of Chinatown.
The suspect was supposedly carrying 50 boxes of 9mm ammo. A box is 50 rounds, and weighs 1.25 pounds, meaning that duffle bag has over 60 pounds of ammo in it. When the suspect tossed it in the dumpster, he easily took it off his back and flung it in.