Since people have already seen me using my motorbike again and almost complaining about my blog still stating that I have problems repairing it: It's all fixed now. Seems like indeed it only was the anker of the starter engine plus the battery. must have been one hell of a short-circuit to first fry the magnet wire and then the battery.
During my repairs I misplaced a washer which led to the blocking of one axis (which in turn prevented the starter engine to do its job). Luckily somebody else did the same mistake before and documented it in some F650 related web forum.