System Architecture is one of the first items that need to be developed. It will certainly evolve and improve over time but ultimately all primary components of the actual functioning product are defined here.
The System architecture is typically done at a higher-level with a further level of refinement as we dive into various architectural components. The system architecture will define what the IoT device does at a system level and then addresses the major components that make up the product and how they interact.
A system architecture block diagram
A preliminary component list
A list of development boards needed for the bench-top prototype