If you've got a basic understanding of PHP,
this tutorial by biorust can help get you started on the basics of a login-style system.
That tutorial gave me such a better understanding of login systems, and has been the basis of my own content management system that i have now applied to many websites, and the feedback has been great.
I've not yet found an open-source CMS that has been all that great. They're almost always a bit of a pain to actually customize. Building it yourself gives you complete control.
I'm by no means a PHP expert, but with a basic understanding of it you can accomplish quite a bit.
Check out Google Analytics for your stats stuff...it's pretty in-depth.