well im going to base it as much from real life as i can, this is not going to be just click and play.
Here are a few features im going to implement:
Loan shark - a user can become a loan shark and lend money, and they set the terms of the deal, if the person dosent pay up the loan shark can then decide what to do
Protection - a gang/family can offer 'protection' to a business ... how they do this is up to them
Citys - Each city is going to have unique features and gangs can take control of them ie casinos, shops, public transport etc ...