Honestly if you are hosting more than one site then the base hostname of the system is somewhat irrelevant unless you have multiple IP addresses.
The reason for this is because you will be doing what is called "Name Based" virtual hosting rather than IP based. What this means is that your server (apache for example) will reply based on the NAME that is being requested as opposed to the IP being requested.
So if you follow along in the how to setup everything to a base hostname (ideally something that can be resolved or Apache will complain but will still work). Once you have the server setup you will end up creating a Virtual Host in Apache for each domain you want to host as it's own site.
This will be the same for Postfix/Courier. The perfect setup is ideal for a SINGLE domain host (or to install ISPConfig which handles all the virtual setup for you). If you want many virtuals without ISPConfig I would strongly advise you merge the perfect setup howto with the Virtual Users Postfix/Courier Mail Howto on this site.
So short answer: I would stick to one hostname (real or fake) throughout the howto. Just pick one and run with it...