Content admin / CMS

Hi, I have a website [[login to view URL]][1] with a chapter "Documentation", including numerous texts The projects consists of making all these texts SEO friendly. The main aspects of this project will be : 1. To edit the cloud of tags related to all the articles, in order to link all the articles having a same tag 2. To increase the number of category to which each article can be linked 3. Each category should be a keyword (SEO friendly URL, description, meta, h1? ...) and gathers all the articles related I am interested by all ideas or best practice experienced in other websites. At present, the website has it own admin in order to manage text and categories. Therefore you will have either to adapt this backoffice or implement a new CMS and link it to the previous admin. Thank you