[RoundelM3]

Buy a BMW "Gold" warranty for the car- you're outside CPO qualifications, so it'd be a good idea to have something to cover the inevitable part failures and resulting repair bills. A lot of things can be DIY, but there are a lot of other things that require special tools or electronic gear to fix. That said, you should also locate a good independent shop that is BMW-qualified for after-factory-warranty repairs. At only 18K miles, if the car you're looking at is in good shape (the same Indy shop can also do an inspection for you), it sound like a great buy. Just be aware of the N54 weak points - HPFP and turbos (mostly wastegate issues), but those are supposed to be covered by BMW out to 110K miles.