Multiple authors with their own categories

I know this might be a tricky question and probably requires a rather tricky solution. But I’ll try to explain as best I can. Here it goes ??

My WP-installation will have a lot authors posting several times a day. Each author should have their own top level category with ability to create sub-categories to it. The author should not be able too see or post in any other categories other than his/her own (when posting).

On the site an author should be able to browse his/her posts and categories as well as the posts and categories of any other author separately. Basically as if every author had his own blog within the blog. So A could view the blog of B and vice versa.

What I would need in order to make this work is:

• A new top level category should be automatically be created when a new author registers
• A way to automatically set a unique default posting category for a new author
• A roll management system that prevents authors to post in any other category than specified

And probably other stuff that I won’t realize until I get there ??

What do you think? Doable or not?