Sorry if duplicate post but the forum isn’t playing nice 8)
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Jurgen, I am not sure why you could not install node.js on your OSPi. My only thought is that it might be an old version of raspbian on your OSPi. I am using the “stretch” version of raspbian and a compatible version of node without problem. If you enter lsb_release -a then it should print out your Operating System version (e.g. Jessie). Let me know out of interest.
Looking at you screen image, you are setting up multiple forwarding rules. Each time you run iptables it adds another rule to the list. So it looks like you create the first rule to forward to port 3000 and then add a second rule to forward to port 3001. But the first rule is still active and because it is first in the list it will always be selected. The second rule will therefore never trigger. So all information is probably being get sent to the port 3000.
If you want to start afresh then you can “flush” out any existing rules with the command sudo iptables -t nat --flush. You can then create the right forwarding rule that you want and then use iptables-save to ensure that it survives a reboot. Does that make sense ?