kalua, once you have these packages setup, do you mind posting a working write up? So that others(and developers) can quickly and easily follow your steps? Maybe even post them in different threads? One for phpmyadmin, one for drupal, etc?
As for drupal, I'd be interested to see how you are going to handle the modules, and the drupal updates. You could also offer drupal 5, and drupal 6 separately. You could have the modules, files, sites, folders as actual folders in the /var/clients/clientX/webY/web folder, and have all of the standard(across all the clients) folders in /usr/share/drupal5/
I look forward to your write up.