Queries regarding Supplier Self Registration

Hi Experts,

I am working on my first E-Sourcing implementation and based on the customer requirements, there are a quite a few points on which I would appreciate getting help/inputs/suggestion regarding Supplier Self Registration process.

1. Can a buyer trigger an invitation mail to a specific email ID(of a vendor) with self service registration URL and instructions?
2. The URL in the above step(1) should have a token/identifier that can ensure that the Supplier registers using this URL only once and no repetitive registration for the same supplier (email ID mentioned in step 1) should be allowed.
3. Once the supplier registers, is there a way to intimate (notify) the approver via email?
4. What is the standard logic on which the user name of the supplier is created in the system? Can it be customized? If yes, how?

Thanks.

Tejas