Subdomains and templating (with forum)

[fatlox]

Hi all,
I’m not asking for a complete solution (this is my job) but, since I’m going to develop a site with complex structure and I use WP only sporadically, I’d like to hear some expert developer opinion on how to design the site.

Briefly, the site will be focused on some different districts (Bologna, Milan, etc…) and will be about 7 main topics (School, Job, etc…).
The site also hosts a forum with about the same categories structure.

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So, the URLs structure should be like this:

mysite.com >> Custom Home Page with main menu for districts and topics.

milan.mysite.com >> District of Milan Home with topics menu and abstract of corresponding forum category.

milan.mysite.com/topic1/ >> Home of Milan Topic 1 with posts and forum abstracts.

bologna.mysite.com/argument1/ >> Home of Bologna Topic 1 with posts and forum abstracts.

And so on.
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Another note: this site won’t be a Blog or Newspeaper, but a guide; there will be a lot of pages and few articles.

As I said, I’d like to know how you would design this site (using WordPress of course!) and which plug-ins would work for me.
Simple WordPress VS MU WordPress, BBPress VS ForumPress, etc…

Thanks a lot to anybody will share his opinion.
Lorenzo