1.When you open an account a number is given to the account holder for the clients to pay, or is it the email address the only identification?
IIRC the e-mail address is sufficient to identify a recipient.
2.How is a button created and put in the Proz page? I have seen that there are several button options: auction, donation, etc., but which is the one you normally put in your translation pages, and what are the steps to follow?
Go to My ProZ.com - My Settings - Personal Data, and enter the e-mail address - that's all.