Creating plugin that will auto add authors by categories

My site is avelim.co.il. The site is on Hebrew wordpress 3.3.2, using the theme Weaver 2.2.6 with many customization done by programmers. I want to a custom plugin created that will do the following: 1. In the edit category screen, there will be an additional menu titled "auto author". Clicking on this menu will show all the authors (including contributors). 2. You will be able to choose an author or several authors for that category, with checkboxes. 3. The menu should be open, so all the authors will be visible in one glance, with no need to scroll. 4. Once you chose an author/authors for the category the effect will be the following: Any time a post is published, with that category, the auto authors chosen will be added as authors to the post. 5. If a post has several categories, it will have all the authors of those categories. For this, I need a custom plugin built. The freelancer should send me the plugin as a zip file which I will install on test site. When the plugin is working properly, I will install it on a live site. The work should be done in 24 hours after being awarded the project. Freelancer should allow 7 days for testing after he finishes his work, before getting paid.