To build on all the great suggestions here, you can install DietPi (a pared down version of Debian), and then use Docker on top of that to run almost any of the services mentioned in this thread on a single RPI host machine.

I run Adguard Home without any issue on an RPI Zero so installing only that on your 4b will leave some performance on the table.

Great idea! Would love to see some screenshots in the readme.