There's a trophy for getting 10 different perks. I think I have 13 or 14 now. Some are pretty easy to get though so you should be able to knock them out pretty quickly. The two I've been trying to work on are the Triple and Quad kill perks, having to do 25 of each multikill. The only place I can seem to do that is in the Fight Clubs. For some reason I can never get the multikills to work the same in the world as they do in the fight clubs. Another one is the zipline assassinations. It's an easy one but i never think to do it when I'm ziplining across the city. Oh yea, the headshot perk is easy to do. I use knives since it's silent and auto aim to chuck a knife at their head.
You're right at the end of the main story Damian. It's not too much more, maybe 10-15 minutes, depending on how long you take to fight Starrick. Like I mentioned earlier, the fight with him is kind of disappointing and was a little bit of a let down, but it wasn't enough to say screw the game cause the ending was too easy or whatever.