Drupal evaluation

Hi all,

I'm doing research to decide which CMS could be more suitable for a complex community-choice competitions system.

I'm looking the most popular CMS as Drupal, Joomla!, Plone, DNN, Typo3 and so on.
I know that there are a lot of modules for each CMS which can cover all my needs, but I know also that the experiences are very important, so I'm here to hear some experiences about Drupal in a context with these characteristics:

1. Multi-site Deployment (mandatory)
Host multiple web sites that use the same installation. Each site will have its own domain, permissions, languages, templates and content. It should be possible for some roles (e.g. super-admin, lead editor, organization members) to use the same login in multiple sites, or better yet, maintain a continuous login session and user profile across multiple sites.

2. Sharing documents and search (mandatory)
In a multi-site context we need to share documents and contents (blog, wiki, forum) across multiple user profiles, sites and (if it's possible) domains.

3. Chatting system
The possibility to have a chatting system among users across multiple sites.

4. Scalable for mass community use
For example, sites will not crash with 100,000 visitors and hundreds of logged-in users using the site on a daily basis day.

5. Multi-lingual
Editor interfaces and content should support most popular languages. Ideal examples would include Arabic, Hebrew, and Chinese.

6. Granular Privileges
A CMS which allow to admin to creating custom user types, roles or groups that specify permissions for what data a user can see, what they can edit, as well as what features they can access.

7. Customizable Contents Workflow
Content approval process should be customizable to include some stages and/or levels of approval.

8. Customizable Form
A CMS which allow to admin to create a form with multiple fields and different input types, browse, search and filter records by different fields and edit individual or a group of records.

Is there anyone which had some experiences with a Drupal in a context with these needs?

Thanks so much in advance for your time and assistance.

D.