Anybody can purchase an extended warranty regardless of the number of original owners.
For a car to CPO'd, it needs to be done prior to the original Manufactures warranty expires and you will have to pay the $450(if i remember correctly) inspection fee. If any items appear during the inspection which does not meet BMW's requirements for CPO, you need to get that corrected (tire tread not sufficient ect..) Once that is done, your car then qualifies for the CPO. Now you just have to pay for it.
I spoke with my SA quite a bit about the M3 issues and he told me he never sees M3's in for repairs other than maintenance and the occasional issue but nothing major. The E90 has in his opinion is pretty bullet proof. He said that if you change the fluids in the car like the pre free maintenance, you will most likely not have an issue. He has not seen a M3 that was maintained like this in the shop. Our area does have a ton of m3's so it is not like they are uncommon here.
12 X5 50i Sport w/ Adaptive drive -- 11 M3 DCT
--- Laid to rest----
2011 X5 50i (Lemon) -- 2008 550 Msport -- 2007 x5 4.8 sport -- 2004 545 sport -- 2002 x5 4.4 sport -- 2001 540i Msport
2000 SL500 -- 1997 SL500