Confused - granting permissions to different users/roles

Hello everyone!

I'm new to Drupal (as you'll see below ;)), and although i find it exciting to work with and explore, there are some things i still haven't fully understand, and i think these are "sine qua non" issues: user/role permissions, categories and taxonomy.

What i'm trying to do is this:

1. I have customers who need some work to be done (don't they all?!), and i'd like to use my website to allow some "working progress" view.

2. Each customer will be granted access to his/her project page (book or story, i haven't decided yet) to view what i write and comment on that.

3. Each project will have more than one task, so i'm thinking of a book, each page beeing a different task of that specific project.

4. When logged in, each customer will have a menu link to this "project book", and won't be allowed to view other customers "projects".

I know this must sound confusing, but hey, i'm confused too! Don't even know where to begin...

Thanks for your cooperation.
Carlos