1 - To get banned means that you'll never be able to play online again they'll ban both your PSN ID & PSID(console ID) & yes you can play offline.
2 - Chances are slight unless you play any of the Call of Duty series or cheat online i got banned for forgetting my Fake plus PSN for a week so this counts too. also do not access multiman while PS3 is online.
Now i am back online, i created another user, how ? i used a valid PSID (console ID) & now i am playing GTA online, Naruto, PES, Last of US, DOA & Batman Arkham Origins & i am not thinking of playing Call of Duty it didn't even cross my mind.
3 - If you're going to buy an original disc & i would recommend you to buy an original PS3 as well, to completely avoid the risk of getting banned.
Because in my opinion its only a matter of time, i am playing for more than a year & i am not banned yet i guess the odds are with me.
I hope this post helps, have a nice day.