Why not contribute or extend existing projects like GrapheneOS or LineageOS? These both have excellent time-tested documentation. If you stay out of the weeds

Why not contribute or extend existing projects like GrapheneOS or LineageOS? These both have excellent time-tested documentation. If you stay out of the weeds in the community and focus on the technical aspects, you can easily get a supported device up and running with your own signing key, update server, and everything else needed. I did for years, before switching to GrapheneOS.