To import the Not Sent extract into a data extension, you need to use three activities in Automation Studio: a tracking extract activity to generate the extract file, a file transfer activity to move the file to the import folder, and an import activity to import the file into a data extension.

Using nested tags to create hierarchies is the best way to minimize the number of tags selected for an asset while still providing the necessary granularity. Nested tags allow you to group related tags under a parent tag, such as "Sports > Basketball > NBA". This way, you can filter your assets by a specific tag or by a broader category. Making the Customer Key more descriptive or leveraging Einstein for content tagging may help with tagging, but they do not address the issue of having multiple tags per asset.

Send Classification is the correct answer. A send classification is a setting that defines the type, priority, and sender information for an email send. There are three types of send classifications: commercial, transactional, and operational. Transactional send classifications are used for emails that are triggered by a subscriber's action, such as a purchase confirmation or a password reset. Transactional emails are sent to subscribers regardless of their opt-in status, as they are considered essential communications. You can learn more about this in the Email Creation and Sending module on Trailhead.

Data Designer is the tool that should be used to create a sendable data extension from various tables including orders, subscribers, and product line items. Data Designer allows you to create custom data extensions that can be used as an entry source for a journey. It also allows you to join multiple data sources together to create a single data extension. You can find more information about Data Designer and how to use it here: Data Designer. Automation Studio is a tool that allows you to automate tasks such as sending emails, importing files, extracting data, etc. Audience Studio is a tool that allows you to collect and unify data from various sources and create audience segments for personalized marketing.

Datorama Reports - Journey Performance is where leadership at NTO should find the dashboard showing the success rate of customers that have been through a Welcome Series Journey in the last 7 days. Datorama Reports is a feature that provides advanced analytics and insights for Marketing Cloud journeys. It allows you to create custom dashboards and reports that measure the performance of your journeys based on various metrics, such as engagement, conversion, revenue, etc. You can also filter your data by time range, journey name, version, status, etc. Journey Builder - Journey History shows the history of journey versions, activations, and deactivations, but not the success rate of customers. Reports - Journey Engagement shows the engagement metrics for a specific journey version, such as sent, delivered, open, click, etc., but not the success rate of customers.