User registration / multisite

I am looking for a plugin, which can ebable me to:

1) Register users through a front page, which can be customized (into an xxx blogging website)
2)Assigns selected usernames as a subdomain of the main domain.
3) Automatically assigns people who register to Author role.

It would be good if people would be able to add their own domain also, and point it to their blog (which would be created on my website etc)

Thank you.