When approaching architecture and design decisions for a large-scale software system, I generally follow these steps:

Understand the problem: I start by understanding the problem that the system is meant to solve, including the functional and non-functional requirements, and any relevant constraints such as budget and timeline.

Identify key components: I identify the key components of the system, including the various subsystems, services, and APIs that will be needed to achieve the desired functionality.

Evaluate technology options: I evaluate the various technology options available for each component, considering factors such as ease of use, scalability, maintainability, and cost.

Define architecture: Based on the evaluation, I define the overall system architecture, including the high-level design of each component, the interactions between them, and any relevant deployment and scaling considerations.

Implement and iterate: Once the architecture is defined, I work closely with the development team to implement the design, and iterate based on feedback and any new information that arises during the implementation process.

In addition to the above, I also make sure to involve stakeholders, such as product owners, other team members, and end-users, in the design process as early as possible to ensure that their requirements and feedback are incorporated into the final design. Finally, I always keep scalability, security, and maintainability in mind throughout the design process, to ensure that the system can continue to meet the needs of users over the long term.