That’s correct! The CLI is pluggable, so if you find an extension for a process manager, you can use it, but the default is systemd integration
Hmm, can you run curl http://127.0.0.1:2368 -I to make sure the Ghost instance is responding? If it works, then there’s an issue with your caddy config, and I’m not well-versed in caddy, so I can’t help 
Hopefully you’ll find the update process to be 10x easier 
The CLI works well, but it is definitely a WIP 
Edit: you don’t necessarily need to use curl to make sure your instance is up, but I suggested it because it ensures that the entire chain of events is functional. You can also use netstat (sudo netstat -tulnp) to make sure ghost is active and listening on the correct port.