There are two or three different takes on the bb-integrated transmission. The one licensed by FSA for the Metropolis setup is a medium duty setup meant for comfort/commuter duty. This new-ish EFNEO, or whatever it's called is a heavy duty one really best used off road.
Good point.gears = more things to break
Quite the litany, all of which I have broken/destroyed and some of them several times. Some have asked why my bikes are clean all of the time and the short answer is "inspection".frame
Differential grade gear oil. Learned that from the users manual of an MZ 250 2 cycle bike I had decades ago.Requires a proprietary frame, though, and being German, requires "Pinion gearbox oil" which is probably some expensive, tough-to-source nonsense that voids the warranty if anything else is used.