If you really want to learn something, make a box that you don't need to work any time soon.. Keep your slack box so you've got a working linux box and then build the LFS as either a seperate box or a seperate partition without getting rid of LFS.
To install LFS, the directions are very easy and straight forward. The real learing experience is to keep a record of all those files it says you installed and learn about each one and what its function is. Read the man pages available online and learn just how those configuration files work. Also, sit down and get comfortable with shell scripts and how they work. First try to follow exactly how your boot scripts work to start up your machine. If you learn this, you might look at slackware's boot scripts and see how they are different. Once you get your machine up and running, learn how to configure and use lilo (the boot loader) and then learn about how to compile and install a kernel.
One of the beauties, imho, is that it is minimalistic. If the box is a server, don't bother with X windows. You should be able to configure and install and run everything from the console (text mode). After you are comfortable with how your LFS system works, you can play with setting up networking on it and all the server daemons you like. With your slack box up and running still, you should be able to take your time and learn how each works one at a time.
I admit, all this was a very steep learning curve for me, but now I'm very proficient in these things.
Also, I'd stay away from redhat.. It seems only admins that don't know much use rh. Some may like it, but it's got so much in it to keep it easy to use that it is a real bear and prone to complex problems. I hate RH, and am LFS all the way. Of course, RH could be excellent for a desktop.. I'm never going to try to install X on LFS.. I don't use it