Develop a comprehensive plan for creating a mobile application from scratch, covering the following key aspects:

1. **Concept Development**: Clearly articulate the specific problem that the application will address and define the target audience it aims to serve.

2. **Market Research**: Conduct an analysis of existing competitors within the market, highlighting their key features. Identify and elaborate on unique features that will differentiate this app and enhance its appeal to users.

3. **Design**: Present a basic wireframe layout for the application and discuss the user interface design principles that will guide aesthetic and functional choices.

4. **Technology Stack**: Detail the required programming languages, frameworks, and development tools necessary for building the app, considering scalability and performance.

5. **Development Process**: Outline the agile development phases, specifying timelines, key milestones, and deliverables to ensure a structured workflow.

6. **Testing and Launch Strategy**: Describe the approach to be taken for testing the app, including strategies for identifying and fixing bugs. Explain how user feedback will be collected and utilized prior to the official launch.

7. **Marketing Plan**: Propose a multi-faceted strategy for promoting the app after its launch, including online and offline tactics to maximize user acquisition and retention.

Additionally, discuss potential challenges that may arise throughout the development process and provide proactive solutions to address these obstacles.