Develop a custom WooCommerce Plugin

Hello everyone, For a WordPress Site using WooCommerce i need a custom Payment Plugin. How it should work: There's another custom written plugin on the website which holds a list of persons names, addresses, email addresses and ID numbers. This infos are saved into the database. (This plugin already exists and is working perfectly). When the custom Payment Plugin (which i need from you) is chosen on the checkout page, the following should happen: A modal window (or whatever) should appear in which the user can select a person from the entries of the other plugin. The user should be able to either enter the ID number of the person, or its first or last name or the address and the plugin should suggest a person which corresponds to the entered infos. Imagine it as an auto-suggest search input field where the suggestions are loaded from the data saved by the other plugin. Then after the user selected a person, the complete order should be processed but the confirmation email with the contents of the shopping cart (the articles the use wants) should be send to the shop owner and SECOND to the email address of the person which the user selected in the step before. In the WooCommerce backend, a order placed like this should appear with some kind of info for the shop owner that this has been a "Consultant Order". The purpose of this plugin is that some other person than the shop-owner gets the order and sends the articles to the user because he has another warehouse at his place. If you have any further questions, please don't hesitate to ask me! Cheers!