‘Out of the box’ EE won’t quite do what you want, but I believe it would be easy enough to tweak it so that it will. Let me run down the basics:
1. - Each division gets a category- that’s no problem. You can create as many categories and subcategories as you need- and each weblog/data container can have more than one category group. The category being 3 pages… well, categories do have custom fields- but likely you’ll handle this by creating new entries and assigning them to the appropriate category. In which case, your category can have as many articles, spread across as many pages, as you need.
2. Using categories as main navigation is a very standard usage- you won’t have a problem here. For example- check out the categories tag.
3&4;. The editing bit is where things get tricky. You can limit member groups with regard to whether or not they can make/edit entries on a per-weblog basis, not a per-category basis. One option would be to make the divisions weblogs instead of categories. However- you can’t ‘out of the box’ allow a group to edit but not make new entries- and in this particular case, it sounds like categories make more sense anyway. And I’m not really sure that it makes a ton of sense to have a member group for each division.
Now- all that said, I don’t think it would be hard to come up with a custom solution for this- using the Standalone Entry Form, a custom member field to indicate which category a member belongs to, and the third party form helper to allow editing.
I don’t want to swamp you with technical brainstorming at this point- but the short answer is ‘Out of the box, it would need some tweaking. For someone well versed in EE, it really wouldn’t be that hard to tweak’.
What I’d suggest at this stage is that you give one of the trial options a run through- see how well you like EE and how well it meets your needs. Once you form a general opinion, you can look for help on the forums on tweaking that last 10% out so that it will do everything you need it to.
Make sense?