configuration and modification of Billing System/Payment Gateway application

We need a good software engineer that will configure and modify a PHP (Joomla) extension application for an archive and back up application. We need this expert to ascertain that 1. the desktop and Web app are synchronized together for exact calculation of ow much space is consumed by individual using the system. The architecture of the system is designed to be managed by a Group Admin. The group admin will have a view of how much space is consumed by the individuals in his group. [login to view URL] individual will also have a report of how much space is consumed and the cost of the [login to view URL] payment system is a monthly billing/payment system. Alert (email and apps) will be configured for late payment after 7days of non-payment (email sent to Group Admin and System Admin and alert on the user's account related to non payment) The Joomla extension has most of the features but some customization may be required. Two Payment gateway will also need to be configured