Depends upon the license you use. Research the GPL, LGPL and other "Open-Source" licenses. You might start here: GNU License List or even: Open Source Approved Licenses.
I don't think you can sell open-source software. The very definition of open-source is Freely available and unobfuscated source code. You can ask for donations, but releasing your software to purchasers only would be a type of "closed" source since not everyone can get it. But like I said, depends upon the license.
You can copyright a CMS by creating one, and then submitting for a copyright. If you don't want people to steal it, copyright it, and then I'd say obfuscate it.
Have a look at the Artistic License. It specifically states that:
"Reasonable copying fee" is whatever you can justify on the basis of media cost, duplication charges, time of people involved, and so on. (You will not be required to justify it to the Copyright Holder, but only to the computing community at large as a market that must bear the fee.)
~Brett