Drupal as an organisational tool and permissions based wiki?

I am working on a project for a design class at school. I will do my best to sum it up in a few lines now, then I can get into questions regarding Drupals suitability for a project like this.

The project is called KorkBord. It is basically an organisational tool that provides the user with their own address book, bookmarks tool, calendar, to-do list and notes section. Everything BUT the notes sections is private and only accessible to the user that created it, but the notes are handled a little differently. The notes are effectively a permissions based wiki content type. The user creates a note and can either make it private (only they can see it), a group accessible note (user defines a group, they can view it) or a public note. That is basically all there is to it.

Now, I THINK Drupal is well suited to this type of thing.

1. Drupals handling of nodes is perfect for this type of application. Every piece of content in KordBord is effectively equal, it simply show different data.
2. With the CCK pretty much working for 4.7, the different node types and fields are not a problem to create and maintain. I finf flexinode a little clunky, and from what I have seen of CCK, it looks very nice.
3. The Views module can restrict the content to ONLY that that the user has created themeselves, making sure there is no breaches of privacy of content leaks.
4. The event module, as well as weblink (I think there is a new one now) and even the to-do modules perform MOST of this functionality already.
5. KordBord is specifically aimed a Australian, New South Wales (HSC) school students. There are HEAPS of us, and it will be quite a high traffic, high content site, and Drupal is well suited to that also.

My only concern is the notes. As it is a wiki, we can already provide editing abilities and revisions, and we have no problems with making the content public or private (with taxonomies and views module), but how do I go about the user aloowing specific users to have access to it? I would like to have the user enter the persons email address who they wish to invite, and, if they are a user, they are automagically added to the list of trusted viewers/ editors for that node, or they are sent an email requesting they sign up, then it will add them.

I would like to use Drupal. it is easy to use, it is VERY powerful and has a very helpful community, but I would like to get your feedback before I make my decision.

Thanks,
Nathan Wheatley