Hello!. So you want to migrate your website to another website url. I know your fear abouth google getting mad becuase of duplicate content, etc. But for those cases there is tem redirections and the permanent ones. Also, webmaster tools gives some options to play the google game well in this migration. We build the new website, place the content but blocking robots. We take down the content on your old website. We upload sitemap to Webmaster tools, ask a reindex etc. After that we place the temporary redirect to our new website and done...well there is some more other thing, but this is just some general than am going to do. I hope i convinced you, best regards!