We don't want a desktop on a server system, therefore we select Custom install on this screen:

Now we select the package groups we want to install. Select Internet station, Network Computer (client), Configuration, Console Tools, Development, Web/FTP, Mail, Database, Firewall/Router and Network Computer server, unselect all other package groups, and click on Next:

The package installation starts:

Afterwards, provide a root password and create another user (e.g. administrator) and click on Next:

Now the installer presents us a summary of the installation and gives us the possibility to change settings by clicking on the appropriate Configure button. First of all we configure the time zone we're in: :

Select your time zone:

On the next screen select hardware clock set to UTC, Automatic time synchronization (using NTP), and for NTP Server choose All servers:

Next we change the Security Level:

Select Standard as the Security level (all other security levels are too restrictive) and leave the field Security Administrator empty:

Next we modify the firewall settings:

ISPConfig comes with its own firewall, so if you like to install ISPConfig, select Everything (no firewall) to disable the firewall. Otherwise, configure the firewall to your needs: