1) Not as far as I know. The debian script you used is also not a official script from ispconfig project.
3) The recommended and most stable Linux distribution for ISPConfig is Debian 6 64Bit. You can use Centos with ISPConfig as well, but it needs more Linux knowledge to maintain it and you might get problems with Centos updates and package dependencies later. If you can not use Debian for your server because your vps provider does not offer a Debian VPS, then I would use the 64Bit Centos image.