First of all, sorry for the fairly long question. When it rains it pours.
Secondly, I assume this issue belong to the WordPress Forums and not to those of BuddyPress or MU. I apologize if I'm wrong. I will quietly, without throwing tantrums, go where directed. Would not like "Hell" though.
Thirdly, for various reasons, not applicable to this specific discussion, I would not like to make use of third-party plugins at all. I have looked at all available plugins (BP and MU) and they will simply not do the job. I will also not have the time to check each and every time whether plugin upgrades (if at all) will play nicely with the Network of Sites. I, furthermore, feel that the core features of WP3 will be more than enough to satisfy my needs. I am not difficult.
I'm using the latest WP3. And the latest BuddyPress. Multisites enabled.
Main site template is a childtheme of bp-default. Main site deliberately putting more emphasys on BuddyPress as this is where the Social/Business Network will reside. People will be able to join and make full use of the BuddyPress features.
Network sites, for a specific reason, will be based on one single theme which is a childtheme of TwentyTen. In this case, more emphasys on WP3, as opposed to BP, obviously, features. Basic WP3 customizations like unique backgrounds and headers will be available. Still one theme though. Those who join the main (BuddyPress) Network, will be able to apply (not register) for their own site(s) [Blogs]. Pretty much a controlled environment.
For the intellectually gifted people within the WP Community, my problem should be a no-brainer. That's why I am wasting your time in trying to give you something else to think about. Once again, not that it should take you guys ages.
My problem is three-fold:
1. I would like to fire the categories as sub-taxonomies of the main category taxonomy on the main site (BP) by means of a function, i.e. the categories will be fixed like Politics, Business, Travel and Tourism, Education, etc. You would still be able to add sub-categories via the Admin UI but they will have to adopt one of these categories as a parent category.
2. I would like to do exactly the same with the Network sites - exactly the same categories by means of a function. Individual site owners would then be able to add sub-categories but only under one of the parent categories.
3. Lastly, once that is done, I need the code to aggregate all the latest posts in each parent category (which would obviously include posts in sub-categories) to the custom font page (home page). The layout and such (magazine layout) is not a problem. Already done that. Just need the code.
Once again, sorry for taking so much of your time. We here in South Africa are in FIFA WC2010 mood and like I said, when it rains it pours.
Thank you for your help.