SME is the server platform to be using especially if you're new to the notion of servers and Linux. I started with SME several years back and got frustrated because it did everything that I needed. So, if you're looking to learn Linux, you should probably try a distro like Fedora, Ubuntu, CentOS, Suse, etc... These are great distros but not integrated and polished of a one-stop-shop as SME. Print out the 6.01 manual and read it 2 or 3 times and you'll get a sense of how complete this server is. If at any time you have questions, post back to this forum.
Good luck and have fun.

By the way, you don't need to install any OS before install SME. SME is built from CentOS and is a self contained server. You have to install it and everything is ready to go.