Thanks to user @aibd for link to this guide Restoring-Stock-Firmware-with-Heimdall about how to use commandline heimdall. It covers much of the same ground as the guide above.
It answers a couple of my questions:
Yes, install ALL the images:
You don’t want to install only half of a section. For example, if you install only some of the files in the BL_ package but not others, you could ruin your booloader and brick your device. That’s why it’s important to specify all the partitions you want in a single command, and never interrupt it.
Yes, you can replace stock recovery with TWRP:
I swapped the stock --RECOVERY partition with a recent version of TWRP, and then used that to install LineageOS. So, I never actually did reboot into the stock firmware