So, how did everyone get the "One Man Army" achievement?
I got it early in the game, before you could cross the Broker Bridge. Instead of trying to drive through the police barricade on the bridge, I took the center civilian walkway, triggered the 6 star wanted level, then proceeded to run to the other side. To the left of the bridge on the Algonquin side is a two story complex with multiple courtyards. I got to the second level and fortified myself in the courtyards, taking out cops as they attempted to enter. There's a Sprunk machine in the courtyard to replenish my health so that helped. Finally after 7 minutes or so I got bored and let a police chopper take me out. Good times. If I wanted to, though, I probably could've held the cops off forever.