N54 Reliability?

I'd like to know from N54 owners how reliable their cars are esp. after 80000kmz? What are their maintenance cost like? I know it will put a smile on my face every single day, I just want to be prepared. If all preventative maintenance is done and I know the vehicle isn't a lemon, am I really going to be sitting with a headache? The car will most likely never be modded but will do a lot of freeway driving.

Any info will be appreciated