Earlier quoted context omitted.
The bootloader is unlocked, thought I don't understand Android enough to do anything useful with that and the Kernel sources. :/ Wish someone would help me. I can provide a build server with 16 GB of RAM and 1 Gb network as well as lots (200 GB) of PCIe SSD space.
Believe it or not 200GB of disk space may not be enough! At least 250GB is required according to: https://source.android.com/setup/build/requirements .
Complete AOSP upto Oreo requires about 95GiB for just the sources + 40-50GiB for each version build.
But most of that repo history is not necessary if all you want to do is build one version. Just clone that one version to depth 1. Nougat weighed in at around 13-14GiB. Add the 40-50GiB for build, and about 70GiB is enough.