S O L U T I O N
Just for the record – may help the community:
Adjusting the contact breaker gap respectively dwell angle of the old distributor fixed the hard start/coldstart problem. – There was no gap at all at no point.
It also solved the rough idling problem right after cold start where I had to pump the pedal for some time to keep it running.
Replacing the worn out old distributor (shaft) (with the 123ignition dizzy) got rid of the occasional misfires.
So car starts and runs well now. Initial curve I mapped is the yellow one (page 1; file attached) I figured out and using vacuum advance (not retard). I will try to lift the curve and play around with it to find the optimal one. As most of the members suggested, it might be happy with some more advance, but for now it runs well, no knocking/pinging.
Valves are adjusted and I will replace some carb gaskets soon + inline fuel filter + air filter.
Thanks everyone for the support again.
BMW 2002A v1.0.123
02sahara's post in Distributor curves/timing for '76 Automatic CA - 123ignition was marked as the answer