Widget availability / Popular Posts across Network

Hi everybody,

I have a couple questions about managing a multi-blog-network. Here’s what I want to have when I’m done:

One main blog at http://www.domain.com/, where

• All posts from all blogs show up
• A widget that displays the X most active posters across the whole network
• A widget that displays a slideshow of featured posts from across the whole network
• A “Categories” widget, that shows posts from all blogs within a couple of network-wide categories
• A widget that displays a network-wide message
• A widget that shows the most popular posts across the whole network

And the sub-blogs at http://subblog.domain.com/, where

• The network-wide-message widget cannot be deactivated
• Other widgets may be edited/activated/deactivated/… to the blog owner’s liking
• the network-wide categories cannot be edited/deleted
• A global navigation bar at the top, where users can a) go back to the main blog and b) choose any author from a dropdown-menu to get to their blog directly

Now I’ve seen that there’s the sitewide tags plugin, but I see a potential problem with the popularity plugin, since – as far as I understand – posts are copied to the main blog, thus being rated there and on the sub-blog separately.

Also I haven’t found any ideas on how to make categories permanent on sub-blogs, or how to have network-wide and blog-only widgets side by side. While researching solutions I find myself locked up in tons of outdated wordpress-mu tutorials, this is really quite frustrating 🙂