Mafia games are old news and people are loyal to old time mafia games like bl and dtm, you will probably start with a small user-base and end up with a completely different site; if they have their way. Stick at it and stick to your guns and in a few years you may start earning.
Overall the profit margins are small compared to the workload, you need to scout the competition and steal their ideas and chances are you will have A S**TLOAD of bitching to deal with.
Over all, i your hoping for a business, you wasted your time. Mafia games are unfeasible...