How can I move my installation to a different directory?
Update the Board URL in the ACP -> Options -> Basic Board Information and move the files to the new directory. You may need to restart the server for the change to take effect.
That's for your first question, regarding the second I guess someone else could answer that
You only need to use the code I posted. That can be the only thing in your .htaccess file, unless there is already a .htaccess file in which case you can add the new redirect to the top of the existing file.