As far as I know, in order to have a webhotel where you do not need any outside servers, you need to have a minimum of 2 servers as you need 2 DNS'es. This could of course be two virtual servers, but the logic still applies. It would be nice to see a tutorial that covers this setup. I realise that there are parts that can be used separately, but it would be nice to have it as one complete tutorial. 1 server with the ISPConfig 3 interface plus billing and using RoundCube as webmail. 1 server running secondary DNS, but controlled by the first ISPConfig interface. Ideally, the second server could also be used for backup purposes. The ultimate setup with ISPConfig would be to just install a basic server, then install ISPConfig and from within ISPConfig be able to add modules and configure everything. But I guess that it is a bit of time until we get there...
Regarding DNS, take a look here: http://www.howtoforge.com/how-to-ru...and-secondary-with-ispconfig-3-debian-squeeze