No options are required, it should just run like that. If you place the service file in /usr/lib/systemd/system/ it should be possible to run:
sudo systemctl enable duplicati
And it will then auto-start as a service.
It does not matter who owns the files, it matters who runs the Duplicati server. If you set up the service as above, it will run as root.
You can then get the tray-icon to connect to the service with
duplicati --no-hosted-server --serverurl=http://localhost:8200