There isn't a fixed offset for any car, and it is a wheel property, not a vehicle property. l
Perhaps more critical but there is still a range of acceptable values. Could you imagine Brabus or Carlsson limiting their conversions to non-ESP cars or only offering wheel options that were within a few mm of the standard MB oem sizes? It just doesn't happen.
Generally replica wheels are far easier to damage and buckle, correct. I have no experience of the difference in ride going from 16" to 18" wheels on a C140 but I'm sure other people have....
But in general, do you get a harder a ride from putting a lower profile tyre on the rims ?
the tyres on mine are 45 profile or 255 x 45, it isnt that bad a ride but 40 profile would be.
jib