Number of points.
Try freeing off the rings by pouring Redex or similar into the plug holes. Follow the instructions on the pack.
Ignore your performance issues until you get the compression sorted. Everything else is a detail.
The E in 280E is not a model designator. It stands for einsprintzung (I think that's how you spell it) which is German for injection. Mercedes did not use E as a model description until the W124.
All engines produce white smoke when cold. It is water vapour. Black smoke is fuel, blue smoke is oil, grey smoke is brake fluid.
Good luck. Remember this is a hobby car. If you can't afford the hobby, take up fishing.