I've tried reading through guides for preseeding and customization, but I did not understand how and where to modify which options. I can only comfortably learn through practical examples, for which I ask this question.

I am looking into preseeding and customizing solution to just do a few specific tasks:

• Completely rewrite the packages installed by default, much like minimal installs and with the --no-install-recommends flag of apt-get.
• Add a few proprietary applications to the default install list
• Automatically install and mount proprietary drivers on install and live session
• Edit the default configuration files for applications installed by default
• Specify partitions along with permission
• Modify the package pool in the installer media (CD/DVD/USB), preferably using command line tools similar to apt-get and aptitude.

Can anyone please tell me how to configure preseed option to only do the above?

NB I do not understand the GPG part after adding/removing packages in the pool.

PS The third point is of particular importance.