Hi! I've seen your requirements and interested in developing this plugin. I've tons of expertise in developing wp widgets and plugins. I have highest reviews for jQuery (frontend), and have expertise in developing responsive templates based on HTML5, CSS3, Client side(JQuery,Angularjs,Backbone) using (bootstrap,Zurb).
I've checked the attached image, I'll use jquery ui for draggable and will start it right away. let me know if u r interested in my bid