Salesforce JBilling Integration

Hello, I want to build a Force.com App for www.jbilling.com integration and want it to be as generic and general purpose as possible because i want to be able to sell it for other customers. I Require a final force.com deploy-able App that we can call it something like 'JBillingForce'. I need your creativity and Ideas on best ways to implement this Integration and make the final app a general purpose and successful appexchange app. Requirements for this work: -Very Good knowledge of Java (j2ee including spring ,hibernate ,grails ,postgresql git ant etc) and JBilling.com system -Good knowledge of Force.com platform including apex, visualforce , Force.com Java API Integration. thanks.