For your first question, epics and stories are common agile practices used in ensuring the successful development of a product. User stories are similar to needs statements in the way that it specifies a flow or task that the end user is to accomplish, and a series of user stories create an epic. When working agile, the scope and scale of your stories and epics will help determine how any sprints it’ll take to accomplish them. If you’d like more details about agile methodologies, you should go here: https://www.atlassian.com/agile/project-management/epics-stories-themes
Regarding your second question, it depends on what type of responsibilities you are looking for in your design hires. If you are looking for someone who can accomplish a very specific set of tasks in a product team, I would say being descriptive would be helpful to the person applying for the role, and to the recruiter who will receive relevant applications. If you seek someone whose responsibilities will range across the various responsibilities I’ve identified (perhaps you’re a startup or consultancy), I’d still try to be as prescriptive in the job title like “UI/UX Designer” or “UX Researcher and Designer”, and again be as specific in the job description.