Where can I find out more about the design and structure of such web application, that implements all of the above efficiently together. To be more specific, I'm concerned with:
1) Database driven XML/XSL stuff. (And not necessarily MySQL, if there are better free solutions).
2) Writing PHP for Ajax (so that scripts only work with data input/output, and do not contain any html stuff).
3) Creating N-Tier application in PHP. I heard about the 3-tier method, which involves the use of some program. I'd prefer to do it from scratch.
4) How to work with CSS on the client side, when dealing with Ajax.
If you could explain it to me, and/or point to some good sources, that'd be awesome.