Large wordpress installs

I recently took over a huge Moveable Type install (over 50,000 entries).

First order of business is obviously to import to wordpress. Due to how poorly the database has been kept, and the “hacks” that have been made to keep everything together, I’ll have to write my own importer.

I’m trying to figure out the best way to organize the site. There are several different sections of the site ( “news”, “opinion”, “sports”, &c. ), all managed by different teams. These teams should only have access to their own entries.

Should I be setting up a wordpress multisite? Or is there other functionality I should be leveraging? I’m pretty familiar with wordpress, but have never dealt with an install of this size.

Multisites seem to be the way to go, except I’m confused how the main homepage would work. Obviously, it will need to pull posts from every section, and possibly combine them into modules like “most commented”. Is there a way to do this with multisites? I also want to assure that a combined RSS feed works as we still have several readers & scripts that leverage these.

I appreciate any help, or resources anyone has!