Hi @yvanm, I am sorry for my poor wording in this post particularly as I (and others) are struggling with Docker at the moment! 
My suggestion was meant to carry the meaning that you could try to build a LineageOS ROM as per those instructions.
(You have dived in the deep end where I cannot assist. I hope your supported device, Galaxy S3, build works out, that’s best way to learn.)
However if you do manage the Lineage build (as it is a supported device there) you will gain experience and have some useful pieces to bring forward to your next /e/ build.
Bon chance