Formulate a design plan for a user interface.
A design plan for a user interface should contain the following components: an overview of the user journey, information on user personas and their requirements, a visual design that illustrates the interface's components and arrangement, a task flow that outlines how users will interact with the interface, and technical details relating to the backend and development process.
The design plan for the user interface should be simple and intuitive, with a design that aims to create the least friction possible for the user. It should be structured in a way that it allows users to access all the features with relative ease. User interaction should be optimized, through the use of visual cues and feedback, to ensure that users understand what they need to do, and how to do it. Additionally, it should be accessible from all devices, as users should not be restricted from using its features due to device type.