There's a lot of plugins and work done in my page. I'm ranked #1 on google, so obviously I don't want to ruin that, however I want to make a clean install and install only the important plugins then importing all the posts. Is this a bad idea? I'm using wordpress, there's a lot of cleaning, I made a lot of changes, plugins etc in these years. Now I just want a clean wordpress blog with a different theme, and the important SEO plugins. Thanks.
It is strongly the best idea to keep the URL's the same as is. You can install a new theme and update the content on a daily basis. Deleting URL's and content is not a good idea. Examples: if one of your pages is: www.examples.com/resume.html you do not want to change it to www.examples.com/resume.html. Best idea is to backup the site files. This includes content, link structure, and meta tags.