For the E60 you can get online fault code tools and find faults.
I have no experience with E60, so cannot give advise, but 460000 Km is of course a lot. Maintenance will be expensive, fuel consumption. If you want to have a cheap and reliable car, buy a Japanese one, for example a Toyota Corolla Hatch GX. I would go for the Hybrid version, here the prices of Toyota NZ for that model https://www.toyota.co.nz/new-car/corolla/corolla-hatch/