How to assign the ethernet interface of the MoodleBox a fixed IP address?
The ethernet interface of Moodle is configured to fetch an IP address from a DHCP server, if one is available in the cabled network. I assume your router has the DHCP functionality too. So the cleanest method would be to tell the router to give the MoodleBox ethernet always the same IP address. Login to the routers web interface and go through its various menues. Usually one can deposit a MAC address and an IP address pair in the configuration.
P.S. This is a new question, which needs its own discussion.
P.P.S. All these are not MoodleBox specific. As I understand, you are doing a community service. That is why, I answered here directly rather than pointing to the appropriate forums. Hope, we don't annoy others.