Therefore I can successfully flash the 0.9.5 NodeMCU which is included in ESP8266Flasher.
When I switch to normal-mode, I'm able to communicate with NodeMCU 0.9.5.
I can do this with Windows, and also with screen/pytool in linux.
I failed every try to flash a custom build FW. I tried a few times with nodemcu-build.com - no FW runs.
I'm aware most esp01 have "only" 512K flash, but my customs are less than 430k.
For sure I tried different baud-rates, but now I run out od idea's.... Please Help!