Hi Paul,
I didn't even arrive on my own firewall, due to the (very basic) firewall of the ISP inside my modem:
Since I got really desperate, 10 minutes ago I decided to add another (dummy) rule to my ISP modem firewall. Afterwards I again rebooted the modem. And now it suddenly works:
I have mixed feelings at the moment: don't know if I should be happy that it finally works ( 
), or should be I be angry for paying a ridiculous amount of money each month to my ISP and me getting a crappy modem with crappy software ( 
).
Anyway port 3001 is now accessible. For the next 4000 steps to get this node running, I will create new discussions 
Thanks to everybody that has been thinking out loud to help me through this hell !!!!
