Here's the thing: you have 18 required roles. Any RP beyond 10 players are already gigantic, let alone 15+, which are extremely rare and most of the time, unsustainable for the long term. In a mechanic-heavy game like Mafia, any one of the eighteen quitting could be devastating. And trust me, it's very common for players to drop out. 

In addition, this setup seems complicated, and could contain unbalance and exploits. I recommend adapting a tried and true scenario from [url=http://wiki.mafiascum.net/index.php?title=Main_Page]mafiascum.net[/url]. There's a few proven setups, many have been played hundreds of times and demonstrated robust balance between factions. Going back to before, I would also pick a [url=http://wiki.mafiascum.net/index.php?title=Category:Micro_Setups]micro game[/url] (9 player max). Smaller group equates to easier administration, and the recruitment target is more realistic.

Mafia games have been attempted here before[sup][url=http://www.roleplayerguild.com/topics/79131-mafia-the-swarm-hunt/ooc][1][/url] [url=http://www.roleplayerguild.com/topics/86012-mafia/ooc][2][/url][/sup], but none of them took off. Outside of dedicated Mafia boards, interest and knowledge about the game is not widespread. With any niche project, the creator should start slow and think small.