Perhaps I'm not qualified to give definite advice but you can have my thoughts!

I have built a dynamic e-commerce site, learning enough PHP/MySQL as I went along. It took ages because of the learning curve!
http://www.wargames-figures.com

Now I'm about to create an entirely different type of site - an information/services/membership type of site. I have decided to go down the route of using a Content Management System and having had a look around I have decided to have a serious go using TYPO3. This is open source and has a lot of documentation and extensions etc. Like any complex system, there is a learning curve but there is only one easy way to acomplish your task - pay someone else to do it!

From what I have seen so far, this seems to be a very mature and solid system and I suggest you take a look at the 2 sites (and the various showcase sites built with it).

http://www.typo3.com/
http://typo3.org/about/

As to the question about xml, I'm sure it could do that but I would have no idea of how to go about it - maybe there is already an extension you could use.

Hope this helps!