We've started by creating an in-depth high fidelity prototype to cover all features and flows, especially to get a better understanding of how to organize complex shopping flows such as product sets, up-selling, and page and component variations for more flexibility for testing.
In this project, I've also had the chance to create and implement a thorough design system, with warning states, status messages, sale countdowns, and advanced interactions, and led the QA process to oversee implementation and integrations for a seamless front-end user experience, especially for mobile devices.