Regarding the SD-card being required for boot, it might not be required at all. I saw this being mentioned on another thread:
[ā¦] NVMe is one of the first devices for U-Boot to probe, and the SD card the last, so you save a few seconds off the U-Boot boot time by not having to let it go all the way through the list [ā¦]
L.E. Oh, wait Jessica is also in this thread. Should have read the thread more carefully. 