As a Microsoft Fabric Analytics Engineer Associate, you are tasked with designing a comprehensive data analytics solution for a marketing team aiming to analyze customer engagement across multiple channels, including social media, email, and website interactions. The solution must adhere to strict compliance standards, ensure scalability for future data growth, and optimize costs without compromising performance. Considering these constraints, which of the following steps is MOST critical to include in your initial planning phase to ensure the solution's success? (Choose one)