1. Customer Numbering
       Check the box: Automatic Customer Numbering in System Options.

2. Collectors
Receivables lets you define collectors and assign them to a profile class or to a customer’s credit profile class. When you assign a collector to a profile class, that collector becomes the collector for all customers assigned that profile class. You can modify collector assignments for your customers in the Customers window and for your profile classes in the Customer Profile Classes window.
Read More @
http://www.oracleug.com/user-guide/order-management/collectors

3. Profile Class
        Use Customer Profiles to group customers with similar credit worthiness, business volume, and payment cycles. For each profile class you can define information such as credit limits, payment terms, statement cycles, invoicing, and discount information. You can also define amount limits for finance charges, dunning, and statements for each currency in which you do business.
Read more @
http://www.oracleug.com/user-guide/account-receivables/1-profile-classes