1998 and 1999 s-classes have no led's in the door handles.
the turn signals should flash 3 times for lock comfirmation.
1 time for un-lock instead.
The alloy wheel standard size is 16x8".
MB uses Textar, Pagid, and Brembo brake pads.
The service reminder (fss) will beep when ign. is turned on.
there will also be a wrench symbol in the cluster display.
Your "red-key" sounds like some kind of aftermarket alarm.
check the underdash for a plug receptacle.
sounds like non-us equipment.