Are people allowed to PM each other/chat on MSN and generally plot with each other out of the thread? Or is that forbidden?
Ans: If their role allows it
And since all the Mafia know each other, can they PM each other and plot who to kill of next out of the thread?
Yes
Also, can Mafia members vote to lynch off one of their fellow Mafia members? Incase one of these Mafia members is revealing too much about their plans, or if they want to appear to be townie?
Yes
Same with a cult - can members of a cult communicate and plan with each other out of the thread?
Depends on the role
Also, when you want to roleclaim, do you have to say the truth and whole truth about your previous role, or can you lie? Can you only roleclaim when you're dead, or when you're alive, or anytime? And if you are a townie, can you role-claim for a mafia?
Depends on the rule of the current mafia game, its different per game
Zorax your making this much more complex than it is, you will pick it up very quickly as the game starts, looking forward to playing with you