I run it in a rootless Podman container using Quadlets. Instead of opening the server’s ssh port, I only port-forward the container’s ssh port (e.g. 22 -> 2222). I have sign-ups enabled, since I want people to be able to contribute (or just create issues). But I have configured the server so that nobody can create a repository. They can still fork my repos and send a pull request.

I have yet to experiment with Actions. I assume the safest option would be to only enable it for my own commits, but I am not sure.

It doesn’t need to know your age. It just provides a way to take a note of your birth date, only if you want to. The system already has a place to write your name and home address. All are optional and practically nobody uses them.

Systemd isn’t an init system. Systemd-init is an init system and it is a part of the systemd suite.