I am trying to do something similar. Except I need to go through a proxy for a whitelisted group of urls. So far, I got Dietpi installed with just a window manager and Chromium.
Chromium auto starts, but because my Raspberry Pi is connected to a managed switch, it doesn’t pull an IP in a timely manner. I saw another post in troubleshooting about this and will work on that first.
I then need to figure out the Chromium resolution settings because the browser isn’t fully displayed. I am sure a homepage configuration setting is in the same file.
Once that is done, I need to create a script that clears all browser history/cache after no input is received for a period. I also need to lock everything down to prevent any shell or filesystem access.
It has been awhile since I have dug into a Linux system, so I think this is a gonna be project. 