FYI, after reading this whole thread and trying a few different approaches, this method ended up being the easiest for me to get OpenVPN working on my OSMC/Raspberry Pi 3. Notably, I couldn’t get the openVPN kodi plug-in working at all.
The only slight variation, since I was modifying the *.opvn file using vi to include the path for the password file, like odin_smash:
auth-user-pass /etc/openvpn/pass.txt
P.S. For some reason, ‘sudo systemctl enable openvpn@vpn.service sudo systemctl start openvpn@vpn.service’ is getting put on one line whereas it should be two seperate commands.