
hey Paolo, ttt/tmo here,
I have a RPi 3 Model B (fourth one of these I've had since 2015), and I am considering running a “from scratch” OS on it, so I can just install apps I need. Right now it is Raspberry Pi OS Lite, which is headless, cli-only, and I think I will start from there and build up. Ful Raspberry Pi OS ran dog slow, which was disappointing as the previous Raspbian OS that ran on the first three model B's was slow-but-usable.
Cool that you got your 400 going, and I, like you, will stick with the REAL Linux machine for day-to-day use (for me it is Debian on a gaming laptop). The Pi is fun to toy with though :)