For the cops, just keep attacking until they die. They have Crushing Chops, which damage you by about 25HP, as well as a less damaging regular attack. You might want to conserve your PP for Captain Strong, who attacks after you defeat the fourth cop (the fifth one runs away).

You will NOT be able to heal up between the fights, so be sure to keep your HP up throughout the battles.

Theoretically, you could probably defeat the cops even at level 1. The main concern is having enough food or PP to heal yourself during the fights.

When the cops are gone, Captain Strong will attack.