Thanks for the long answer Petefoth.
Just some thoughts on updates at L4M: As you start the build cycle on the 1st of the month - you will have the security updates from the month before. So if the new updates come out on the 20th. (for a late phone in the build cycle) you will have security updates about 50 days late.
If you would start the build cycle on, say
15th of the month, the LineageOS ASB (security update, see https://archive.ph/divestos.org/pages/patch_history) are usually already merged. So on the 5th of the new month (15 + 20 (days for building) = 35 = 5) the new released update would only be 35 days late - so the security updates would normally come about 15 days earlier.
I hope I have made myself clear.
Is it possible to lock the bootloader on L4M (Pixel 3)?