Cross-Platform Social Networking App

I have an idea for a full-featured social networking product and need an experienced developer to turn it into a polished, cross-platform application. The core experience centers on user interaction and real-time engagement, so performance and clean architecture are priorities from day one.

Key functionality:
• User profiles with avatar upload, bio, and basic privacy settings
• Real-time messaging (one-to-one and small group) with push notifications
• A scrolling news feed that aggregates posts, images, and quick reactions

Target platforms are iOS, Android, and a responsive web app. A single shared codebase (React Native, Flutter, or similar) is ideal, but I’m open to native approaches if you can outline clear advantages. For the back-end, I’m leaning toward a cloud-hosted REST or GraphQL API—Firebase, AWS Amplify, or an equivalent stack would fit—yet I’m happy to consider alternatives you recommend.

Deliverables at completion:
• Source code and build scripts for all three platforms
• Deployed back-end with basic authentication and data models for users, messages, and posts
• Brief developer guide covering environment setup, running the app, and publishing updates

Please include examples of past social or chat-heavy apps, estimated timeline to a usable MVP, and any suggestions that could improve scalability and security.