When architecting a professional Gatsby website, it's crucial to select various systems such as a build and hosting provider, headless CMS, component library, e-commerce platform, analytics, authentication, search, and forms, as well as to establish effective workflows involving these systems. The interaction of these systems and workflows constitutes the architecture, often overseen by a team or tech lead. Although architecture can be complex, it doesn't need to be finalized before a project begins, as teams can benefit from parallelizing development and architecture processes. Resources such as blog posts and documentation offer best practices for optimizing systems and workflows, including CMS-driven landing pages and CMS previews, enhancing site performance, and ensuring a robust product experience. Sam Bhagwat, cofounder and chief strategy officer of Gatsby, emphasizes that architecture decisions can be made incrementally, allowing teams to develop components while simultaneously determining their CMS and hosting solutions.