bemdesign on "Managing Multiple websites for clients ?"

Hi all,

I would please like to know if:

1. is it possible to manage several wordpress sites for paying clients in one place through some sort of global dashbaord.

2. Also Is it possible to set permissions, so that you can give a paying client access to your global control dashbaord, but so they can only access their site to make changes?

3. If you have some kind of global dashboard for all your paid client's websites, how do plugins work, do you need multiple versions/installs? Same question for analytics?

4. What happens to databases when you have many sites? Is it necessary to have separate databases or separare instances of wordpress installed on server for each client?

These things would be very useful if managing a web development business, both for the client and for the service provider and I am dying to know how to do the things mentioned above. I am very much looking forward to hearing back from you, thanks so much guys.