From my experience, the installer doesn’t update users/passwords for the web interface for a re-installation. It just does it for the first installation.
The FTP Path issue is more concerning to me. @Developers
I also updated that part of the WiKi with this info:
https://wiki.fogproject.org/wiki/index.php?title=Troubleshoot_FTP#You_must_first_upload_an_image_to_create_a_download_task