You could go into their wiki. It's linked from the page, and skim/skip over that installation stuff, until the chapters where they explain what they did to the kernel(s), how they compile and link optimized, schedulers, and stuff. It's not ultra-thourough, but gives a good overview.

I've settled on sched_ext: BPF scheduler "bpfland_1.0.18_g5bff813c_dirty_x86_64_unknown_linux_gnu" -powersave for processes, and let mq-deadline handle internal storage, and bfq anything connected via USB.

What do you mean by "stable"?