Help with upskilling myself and writing roboust backend

I’ve recently been tasked with writing the backend for a full-stack web application for a client who runs a offline travel agency. With a possible user base from 10,000 to 15,000 users and potentially more in the future, I want to write a scalable and a secure backend

I have a good understanding of Django and Django REST Framework, having worked on two previous projects, I’m looking to upskill by diving into more advanced topics related to scalability, performance, and best practices for handling larger user bases.

provide me with some good resources, tutorials, or advanced learning materials that will help me:

Build scalable Django applications.
Implement efficient database management and optimization.
Enhance security and performance for a growing user base.
Leverage Django REST Framework for high-performance API design.

Any guidance or suggestions would be greatly appreciated!