Do you have an option in createaccount.aspx page where customers can select which customer level they want to be assigned to or it's a discretion of the admin user?
Not probably an approval request, but just a simple notification to admin when someone registers? You can use the existing appconfig: SendWelcomeEmail logic and add the admin user to the recipient along with the customer's email address.
Open createaccount.aspx.cs file, take a look CreateAccount() method under
Code:
if (AppLogic.AppConfigBool("SendWelcomeEmail") && EMailField.IndexOf("@") != -1)
You can also check appconfig: DefaultCustomerLevelID parameter.