My suggestion would be to install Ubuntu server (or another distro) and use it for sonarr, radarr and other *arr apps. I do the same with a old laptop connected to a nas for storage
Edit: look for the trash guides for more information and help setting it all up
For self hosting plex, sonarr and radarr etc... I recommend the trash guides. https://trash-guides.info/ When you don't want your self hosted apps available from outside your network you don't need nginx. And for the port security, as long as you are not port forwarding there is no security issue. Keep in mind that when you host things on your local network that other people on your home network could be able to access your apps. Which is not a big deal when living with family or on yourself.