looks good, although for others following in your footsteps it is worth noting that
… overrides the default ‘journal’ setting for systemd (which uses journalctl for logging rather than the old syslog service).
For others doing a self-hosted install, note that ghost setup is there as a convenient way to create a standard install and all the setup stages are optional and can be skipped if you prefer to do it by hand (Ghost-CLI - A fully loaded tool for installation and configuration for more info). It is hard to see how the sudo dependency can be avoided in this type of utility since root access is needed to set up nginx, systemd etc.