Hi Malte,
a) You can play around with some parameters defined in the dotlrn package: subcomm_pages_csv, club_pages_csv, user_portal_pages_csv, class_instance_pages_csv. In those parameters you can change the number of pages and the layout for each page.
Now, if you want to change the portlets position, then you could modify the ad_self_to_page proc defined for each portlet, so you can indicate in wich region and what page do you want the porlet to be added. Im not sure if there is another way of doing this.
b) I have been working on a new interface for adding portlets to the default portal templates, but it has not been contributed yet. Also I implemented some functionality for applying a given template to a group of users/communities/subcommunities. Maybe this new stuff could work for what you want to do.
Regards,
Victor Guerra.