Ok so, here's an idea that I came up with involving some of the ideas so far.

What if we start this off with everyone getting an invitation to a criminal boss's house. this sort of invitation could be by word of mouth or what have you, and this way people can be like "Oh, money is involved... let's do this shit!" I feel like it could be Roxy's family that could host this 'party' with promises of a cash reward for all participants. The entire city could be run by a large mafia or something like that. This mafia could have control over a TON of things, and Roxy's father (or who ever we decide fits the bill) will have this plan to take him down via using all of these different characters we've made to help him. We can plan out the tactics later I suppose, but this would get everyone introduced, and then in the middle of the big take down plans things could get ugly. NPC's could wind up dead, and the gang sort of decides "Fuck this, things are getting too weird" while other people are content with the gang and decide to stay. From there on out, it could be an all out war.