Hey Fab,
I dont recommend going straight to RUTX14 if you havent managed to get it working with the RUT360, because probably you will have the same issue.
Its strange that the LAN led doesnt blink on the RUT360 when connected to the USG device, you can check on the USG device if auto negotiation is enabled on the WAN port, or if it is set to 1000mbps, because if so, you have to set it to 100mbps full duplex, otherwise they wont communicate.
Also, the WAN port on the USG has to be configured as DHCP, because it has to request an IP to the RUT360.
If nothing of those works, i'd recommend you to talk to some IT Consultant.
Best regards.