What I am looking for is as specific and detailed information as possible on
how to go about building a functional Linux OS derived from an existing
distribution that will run on an embedded system (say an ARM product).

Lots of related info is here:
https://elinux.org/
https://elinux.org/Boot_Time

I am interested in the high-level ideas nad philosophy of booting embedded
systems, and on the details that follow.

The web is cluttered, so I figured I'd ask here. Thanks.