Question about Root and User accounts

Hi,
I have been an admin for several years on win and mac, but am very new to Linux.

I just want a better environment to run and self host my sites and email.

My first question is: Is CWP actually meant for what I want? In looking up how to do things, I seem to get the idea that this is meant to be a front end for if I want to sell hosting and manage customers. Can someone set me straight on this?

Anyway, my main question: Since setting up the system as Root, I didn't see the need to set up any other users. But I found in order to set up a domain, I had to set up another user besides Root. Why does a domain have to be tied to a user?

The problem I had was that when setting up, I made HostName and ServerName mydomain.com, then when I tried to actually add the domain and was taken to the user set up, it would not accept the domain and gave an error.

Can anyone help me with this?

Thanks very much!
Scott