Regarding the network key, that’s something you need to randomly choose yourself.
See here:
and here:
You need to set the network key in your configuration.yaml and then re-add the node(s) “securely”.
Remove it before re-adding.
This applies to all ZWave nodes that should use a secure connection.
In case of the Aeotec: when it’s added securely, it will blink blue when it detects motion.
If it’s not using secure communication, it blinks green.
Sebastian