Keith,
I haven't played allot with RHEL flavors very much but. If I remember correctly, to create a new user on a RHEL system you us useradd while in Debian/Ubuntu you use adduser and the home directory is setup for you. Such servers like Apache or SSH are not installed from the beginning.
But since I've only used the desktop version that might be different if you are using the server addition. So your build is correct it's just that in the main two families of Linux, e.g. RHEL vs Debian. There are going to be differences in 'some' commands. As for packages I would image it's a difference from desktop vs server, if not then its the same as the commands.
Hope this at least answers some of your questions. Allow be prepared for some packages you used in RHEL not to have or hard to find dpkg packages.