Stream profile vs redirect rewrite in http profile vs proxy pass irule

Questions 1 & 2 answer: HTTP request line and headers contain the hostname/path/file.html information that you may wish to rewrite to match the path/filename used on the server side. In addition the actual page that the server responds with may contain links to other parts of the application that need to be rewritten to the client-side naming convention. This is header and content (body) rewriting.

Question 3 answer: the client never sees the server port number only the virtual servers port. I am not aware of any standard HTTP response header which would contain the server port though it's possible your app might be doing this. You should consult with the app administrators and developers to determine this.