Site review

I am going to build a social networking site, and instead of building it from scratch I am going to use an existing social network that I have. ( the new site shall have more or less the same functions as the old site, but new design) Before I start rebuilding the existing network, I want to make sure that it is good enough to base a new network on. ( so that I don't build the new network based upon something that is poorly built) For the existing? social network? site? I believe that one problem is that the design elements are placed in the same files as the actual code. I have received advice that this is not good, that it is better to have all design elements in a separate file. So my first question: Is my plan correct: 1. To start with cleaning up the files I have and separate the design in a separate file. 2. To implement the new design by creating/modifying the newly created design file If there is a better way forward please advice. Second question: If the plan above is correct I need someone to make the cleaning of the files for me. So that I have one design file for all pages.