Populate Joomla from from database

This is for a customer of mine. His site is going to be a Joomla 3.4 site. His clients bill him for work they have done for him. Each client charges him a certain rate depending on the task completed. For example they have an Attendance Rate for Day Rate , and one for Attendance Evening Rate. They will have Billing Codes for Direct Exam Rate, Night Rate, Copy Sales rate. 1. I have changed the Joomla registration form to include the the rates but I dont know how to validate them. I need the validation accomplished. 2. When the client logs in he will be taken to a page (see metrosuccess attachement) where he can choose to change his profile, submit an invoice, submit an invoice with and attachment. I can create the invoice form but I need it populated with the clients personal information from the database(see metropersonalinfo attachment) including the rate fields. Then calculations need to be made. For example, the client with enter a Attendance Code,and that will cause a subtotal. He will enter a Billing Code and a quantity and that quantity will be multiplied by the Billing code Rate to come up with a subtotal. There will be several sections like this. At the end all the subtotals will be added together a grand total and the form will be submitted to the client (me for now