Create a simple WooCommerce Plugin

On my website [login to view URL] i sell audio files. I need you to make a plugin which will allow me to add an extra option to existing WooCommerce products. All my products as "Simple Product, Virtual, Downloadable." So that means that my products are 100% digital and staight after purchasing product clients get a dropbox download link for audio file ZIP archive. I need you to make an extra option in admin panel where i add Product details (Admin panel-Products-Add Product,) as seen on screenshot. There must be 1. Price of extra option 2. Type(class) of extra option. In my case it's just a PNG image which will be next to 'Add to cart' button on shop's page (see screenshot). In admin panel you can make a dropdown or checkbox with 5 type(class) options. 3. And link for purchased file (integration with dropbox plugin which is already installed into my wordpress) So in the end result, when client adds product to cart, goes it cart and he can choose if he is willing to pay for this extra option or not. If yes - then subtotal amount on cart page will increase and after paying an order he will recieve downloadlink for that extra option. I use only paypal as my gateway so that will make things easier. The result of this task can be seen on [login to view URL] I need to make same thing. Check screenshots, i tried to visualize as much as i could :)