Ok I have a killer now but where I got hitman contracts? I don't want Mabuta as first mission, probably it's too tough.
Also, what my gang leader doing? Right now I see no point at all.
There is a way to get contracts on specific NPCs but you first must have them in your 'Enemies' list. I'm not sure how many ways you could actually get that to happen but one way I found is to blackmail a girl with the sex tape and try to have her become your whore... if she refuses and says 'then you get nothing' or something to that effect, she should become an Enemy of yours... Going to the 'Enemies' section & to that NPC you should then have this screen:
Make a contract on that NPC then go to your killers and you should see this option:
which leads to:
As for the gang leader role, I'm not sure what his purpose actually is. I haven't found anything to do with him nor can I tell what stats to look for. I personally put a guy that can shoot, can drive, is physically imposing & has some decent corruption & dom stats. Not sure if it does anything though.