Thanks for taking the time to reply to my questions. All makes sense. I wish I could get Debian set up in 20mins! Last time I tried, I struggled to get wifi working. I’m going to have to get familiar with setting it up with a bit of trial and error and just use ethernet for the initial setup I think. One of the main and significant benefits of having an SD card inserted in the Pi4 with a working bootable “image” of the attached USB SSD the system boots from is that if there are any issues with the USB drive or an update goes bad I can just remove the USB, boot from the SD card and then clone back to the USB SSD. I’m setting up a HA system for non-tech savvy people so having a failsafe like that is very valuable. Off topic though!
Debian 10 64bit. I have searched for an answer but can you or someone else point out what might be obvious in how to get the 64bit version of Debian installed on the Pi4? Is it just a case of using a 64 bit kernel like with Raspberry Pi OS?
EDIT: I’ve realised that following the instructions as-is installs 64bit and I’ve got a fully working, stable and supported installation! Thanks @kanga_who!