@hi first gen: emulate how this’d work. Qemu or vitualbox or docker or etc. trim down, and choose between stripped Linux/bsd OS and a genuine bespoke ssh-only OS — my vote’s on the latter being a bad choice due to challenges of owning ssh, drivers, patch.

Second gen: any odd bit of salvage / surplus HW fitting your plan. Hone in on cpu, I/O.

Third gen: a thing. Esp32 gets you WiFi Bluetooth and variety of screens, pi zero gets you hdmi. This oughta be in your mind at gens 1 & 2, including ‘to Bluetooth or not to Bluetooth’ since a freakishly-portable term is going to double usability if it readily hops between minimal config and kbd (mouse?) bigger-screen via hdmi & bt.

#goodLuck, following.