As for how long they last, there's no right answer. When I used to commute 15 miles using back roads, it was 12k miles on a set of front pads and 24k on the rotors. Lots and lots of braking. 1983 300SD.

Now my commute is 12 freeway miles and I brake maybe 6 times....looks like 30-40k on a set of front pads, and lots more on the rotors.

In CA shops that machine rotors will usually measure yours and tell you if they can be turned, keenly aware that lawyers will be all over them if they go below the stated minimum thickness and you have an accident.