Import PHP/XML Code into a new WordPress Plugin

My website offers a comparative rating service where users may enter their state of residence and five characteristics about one or more horses they wish to insure and obtain an instant online quote for equine mortality insurance from up to six different companies (a live example of this may be found at [login to view URL]). The user may then add "Optional Coverages" to their mortality insurance quote on a horse by horse and company by company basis. The optional coverages displayed for each horse are dependent upon whether or not that horse meets the eligibility criteria programmed into the rating code for each of the six insurance companies (state of residence and horse’s age, breed, sex, use and value). This code currently sits outside of WordPress in its own directory. When users access these pages, they are actually accessing a stand-alone PHP / xml project. I want to integrate this project into a WordPress plugin (both the PHP and XML pages). This will give us the ability to require users to register for access and authenticate before obtaining the quote. It would also allow users to store the quotes they receive to return for later use. We need to have different levels of user roles (subscriber, agent and administrator), each with an increasing level of rights. Subscribers need to be able to prepare new insurance quotes and save the quote (or quotes) to be accessible on a return visit. We need to be able to turn company programs on and off for Subscribers. Agents (a custom user role) should have subscriber privileges, along with the ability to store and recover quotes by customer name. We need to be able to turn company programs on and off for Agents. Administrators should have Agent privileges as well as the ability to store and recover quotes by Broker name as well as customer name. We need to be able to turn company programs on and off for Administrators. We also need an admin control panel that will permit us to update rates and coverages as well as allow us the ability to add new programs as they become available to us. The rating rules are contained within a handful of PHP pages, and the info referenced by these pages (ages, breeds, sexes, uses/rates, endorsements) are all contained in XML pages. In total, there are about 25 PHP pages and 80 XML pages.