When you are done you could have a look at these two projects, they are both open source and free. You should be able to build something around them.
1.) vtiger Open Source CRM
A very nice CRM system that already has Joomla hooks.
2.) CiviCRM | CiviCRM Community Site
CiviCRM is an open source and freely downloadable constituent relationship management solution.
Let me know what you think.