How should I be writing the latest distro ISO to a USB for install?
Follow the wiki. It shows you step by step.
Something must not be working correctly. It looks like it installs fine but I get the Unable to Generate MOTD error when I log into Root.
I used Rufus https://rufus.akeo.ie/ to create a bootable USB stick of the install image and it worked perfectly.
The only issue I had gettng FreePBX up and running was properly configuring the DNS servers, which I resolved after reading this thread:https://community.freepbx.org/t/freepbx-distro-activation-loops/30381 , although I doubt that misconfigured DNS is the source of your problems.
Try a fresh install using Rufus with the “Create a bootable disk using DD image” option and see what happens…
Seems my problem is the i219-v ethernet on the NUC not being supported by centOS.
What version of CentOS are you using? If it’s CentOs 6, I found this guide to rebuilding the linux kernel to support your NIC, but it is rather intensive, requires some knowledge of the command line, and can potentially bork your kernel, so proceed with caution.