Gangs will automaticly be created, cause a lot of players prefer to be togheter in small groups to protect themselves.
Having more advanced gang abbility is a good thing though. Like having official gangs, But anyway I don't think it really matters, there will be gangs anyway. If there exist gangs, the biggest thing, would be an easy comunicate with them.
Also, gang wars is a good idea though. Having three groups that spawns at one island each. Each gang should defend their own island, And the one that is standing in the end is the winner, Like last man stand, in Unreal Tournament. And then ther could be other game modes to. But whatever.