I find it hard to start doing the actual work.
I’ve started to create the two necessary files for the FP3. But I’m already somewhat stuck at the first step 
In the flash-scripts repo I see that there were recent changes with message “Add FP3 scripts” (does that mean someone at /e/ is already working at FP3 support and my efforts are wasted?).
So I copied those over to the installer repo.
Looking at the existing samsung files, they first wait for download mode, so I assume I’d have to start with wait for fastboot mode. But I don’t understand what the DEVICE_LOCKED_PATH device lock file (typically ${DEVICES_LOCKED_PATH}/${DEVICE}) parameter is supposed to mean.
I could do with a little more guidance than reverse-engineering from devices I don’t have and that use a quite different way of flashing than my FP3.