Need site-setup-ideas for a "multi-site"

I'm looking into building a website for building-code-issues (more or less :) - non-commercial, citizens-awareness-type). I'd like to collect your ideas as to which type of "CMS" setup I should look into (e.g. dotnetnuke, etc.).

Here's the general structure I have in mind:
a) General section - with news / documents / links / forum / comments / calendar
b) Specialized section:
    - Group per geographic region
         - Group per specific location
              News / documents / links / forum / comments / calendar
              Group admins / moderators

I think the general section should be more or less clear :). The specialized section should be split per geographic area and then also per specific location in that area. I.e. you should be able to choose a general area and then a specific site in that area. To this specific site you will then be able to post news, documents, links, have a forum, comments, calendar, mailing lists (+ whatever's fun) + have it admin'd by some group admins.

Does that make sense so far? :))

My setup: I have a win2k-server with mysql/mssql/asp.net/php, etc. awaiting the site :). I would prefer something with asp or asp.net, but that's not the requirement.

Is there anything out there that can be customized to this fairly easily? Or would it be best to use something like dotnetnuke and set up sub-sites for each specific site also with dotnetnuke (manually... )? Any ideas? Or should I forget about using/customizing something "off the shelf" and start coding my own?

Thanks for your comments!