I think that error is related to a missing dbus session but don’t quote me on that.
You will probably find it easier to use a system level service, but run it as your unprivileged user with User= and Group= directives. Once you get that working, there are various other parameters you can add to harden the service if you like.
This is a good reference for hardening: https://docs.arbitrary.ch/security/systemd.html
The arch wiki has a good general reference for all things systemd: https://wiki.archlinux.org/title/Systemd
To start small setup a static website behind nginx. This requires you to create a basic website or copy a template, it goes somewhere in your filesystem, in linux /var/www is common. Once you have that, setup the nginx service and point it to that location. You can do this locally then expose it to the net or put on a VPS. Here is a dead simple guide presuming you have a remote server: https://dev.to/starcc/how-to-deploy-a-simple-website-with-nginx-a-comically-easy-guide-202g
Once you have that covered, ensure you know how to setup ssh keys and such, then install, configure, and run services. From there, most things are easy outside of overly complicated configurations.