The Chorus 2 web interface provides only a subset of Kodi functions. Maintaining add-ons doesn’t seem to be possible in Chorus 2 and needs to be done via the main Kodi interface.
The “Websocket failed to connect” message is a known issue, but doesn’t seem to affect the functioning of the interface.
Switching off CEC can be done via the main Kodi interface. See Disable CEC. Again, I don’t think this is possible via Chorus 2.
I’m a little surprised you’re saying that the default web interface port is 9090. I did a fresh installation of build 2018.07 and it was on port 80.