@sycohexor: I think you'll get what you need for a working image by selecting the correct target, but not much more. LuCi has to be selected explicitly.
I've finished the first version of the guide: https://lede-project.org/docs/user-guide/beginners-build-guide
Let me know what you think. The goal is to give anyone the bare minimum needed to start building their own firmwares.