Custom Wordpress Plugin to Insert Content After Post

Hi Freelancers! I would like to create a Wordpress plugin that will enable me to add a line of text to the end of every post. From the plugin page, you can do 3 things. 1) Add new custom lines of text 2) Assign posts to each line of custom text via a drag and drop selector. The custom text would then be added to the bottom of each of these assigned posts. 3) View existing custom lines of text created. When I click on a custom line of text, it expands to show me the list of assigned posts. Let me know if there's anything you need to clarify on. Thanks!