How do I make sure all my customers are getting called?

How do I make sure all my customers are getting called?

I'm in the process of setting up Zoho CRM to manage my sales business.  We are a B2C company that sells many times over to the same customers.  When a customer reaches a certain sales volume, they are assigned a regular sales agent.  Until that time, the customers are all shared equally among all sales reps.   They focus on calling the customers that haven't ordered in over 60 days and try to bring them back to us with a new order.

If I import all of these customers in as "contacts" and any orders they have placed as "Invoices", how do i make zoho give me a list of any "contact" that hasn't had an "invoice" created in over 60 days?  And how do I let all of the users work this list?   What module would this list be in?  Do I create a "Potential" for each "contact" that meets the criteria?

Any help getting me on the right track would be appreciated.

Lance