Talon isn't evil, per say. Kavyn failed him. He nearly got Talon caught, and cost him the food in the process. He was of no use to him. So Talon killed him, ironically, with the dagger he abandoned Talon for. Regardless of whether or not he was right, it was the concept of strength and survival drilled into Talon's head. Is it murder? Sure. Is it evil? Not so much. As other people mentioned, he didn't torture him. He just knifed him. It was a 'survival of the fittest' type act. Now, am I biased because I am a Talon main? Probably. But anyway, 'evil' wouldn't quite be the correct term. Perhaps 'cold'.
As for his victims, I am almost 100% certain gender does not play a role to Talon on his targets. If Marcus DuCouteau says kill this person, Talon will.
As for the sewers, it actually makes plenty of sense. The authorities aren't going to be combing the sewers in case of a dead urchin. Even if they saw a body of a dead urchin, they'd probably think 'good riddance'. After all, the urchins are the ones stealing the food. And I doubt it was just Kavyn that was put in the sewers. One of Talon's quotes is, "Another body for the gutter.". So the gutters or sewers were obviously a fine place to dump a body after a successful kill.