I'm also interested in smartphone operating systems like Ubuntu Touch and postmarketOS etc.
- make sure bring extension chords, and make sure you have enough fast wifi for all participants
- bring enough USB-s. Installation on older laptops can take time
- ventoy is useful
- for beginners stick to Fedora/Debian. Popular distros come and go, but these two are constant and will be supported for a long time
- don't give options to beginners if they don't ask for it. You will induce paralysis of choice
- automatic dual boot setup by Debian installer works very well. Partition shrinking on Windows isn't scary as I thought before
- sometimes you can't install BIOS/UEFI drivers without windows (on older devices). You maybe want to do that before installing Linux
- i think it is good to have a windows installation ready. At least for windows boot loader recovery if anything goes bad
- bitLocker can be PITA. Don't lock users device
- after installation update system
- write some material, what-to-do-after-installation guide, and give to participants. Maybe create group on some social network or messaging app
First time users might appreciate seeing the USB drive method since that's probably what they'd attempt next time at home.