Clean, Tidy and Improve existing HTML/CSS

I have a Website which has been designed in such a way that every page is within its own folder, and has its own on-page CSS. Also, the naming conventions for all pages and images are very poor. I would like all HTML to be cleaned, tidied, all placed in the root folder, with one master CSS file. Also, all page names and image names should be shortened and improved for SEO purposes. The HTML and CSS muct be W3C valid. There is no design work required here, its just a clean up thats required. We will have more sites which will require this treatment in the future.