Convert project to Wordpress Plugin

I have a currently functioning PHP/Javascript project designed to implement an online payment process via the PayPal API. It contains several php files, creates/utilizes 5 MySql tables for storing order information (managed in my code), and manages about 20 configuration options to customize the process. The tables and configuration optons are all created/managed from a simple-to-use browser interface, but I will consider changing this if necessary. I am looking to have this project converted to a Wordpress plugin. The current process is managed primarily as a couple of PHP classes, with exposed functionality that should be easily maintained/utilized when included in the plugin. I expect the plugin will primarily be a wrapper for existing functions, and I don't expect any serious difficulties, but I will be available to make any coding changes to my code if required. Thanks