I didn’t know about osmin! I might try it out.

For the poweroff, I’ll just poweroff the Pi from the UI and wait a sec for it to go down. Initial testing has me waiting 10 seconds on the “shutting down” screen. That’s short enough, meanwhile I can put my jacket on or something. Once off, I just unplug it. It’s also running on SSD because I don’t trust SD cards to endure constant read/write from satnav so I installed from SD card and cloned the OS to an SSD, it should be more resilient this way.