How many "client accounts" can a supplier have?

At our client we will have suppliers with multiple client accounts. Each client account will have a seperate bank account. Potentially a vendor can have over 500 000 client accounts.

A client account can either be a site or just a bank account under one site. How many client accounts (sites / bank account) does Oracle support?

How have other dealt with vendors with mulitiple client accounts?

Thanks in advance.