Terrible Advice. Stay entirely away from Slack, or Gentoo. Work with Red Hat, or, if you must, Debian.
The elitist will say "but you wont have the fine grained understanding of everything." But that is the point. You never will. And if you teach yourself that you have to know everything, then when you have to set up servers that are used, by organizations, in the real world, you are going to not know the tools that exist to help you. You will feel bound to "if I didnt do all of it, I can't understand it."
And either you will just do what you are told, and do a lousy job, or you will make a system that is near unuseable for general purpose.
Learn your way through Red Hat, or Debian.