Onn Android boxes work well for my parents. As long as you install Projectivy launcher to get rid of ads and clean up the UI. I make it so there are three app icons and nothing else on the screen, then it's easy to understand and navigate.
My two most popular public game servers are Necesse and Rimworld Together. Neither have many public servers.
I think you want a skeleton. /etc/skel
If you want to copy settings for Firefox and other applications, copy (parts of) your .config in there. When you create a new user it uses the skel directory as a template.
Google/GPT will explain it better than I can.