If you dont plan to get the maint along with the CPO then dont get the CPO. Aftermarket warranties like EasyCare and Zurich are far more superior and much more bang for you buck.
Brake pad life is dependent on driving style. You drive highway, they dont wear fast, you drive city they wear faster. You track, they wear fast. You cruise they don't wear as fast. If they are at 50% dont bother, you still have a while.
SMG Clutch - No one can tell you when it will need a replacement. It can go out at 30k it can go out at 60k it can go out next week it can last 80k also. So you can never tell when time will come and you would need to do the clutch.
Extended service / Maintenance Package plan from BMW covers both clutch and brakes