'Update Email Now' needs to be applied to each email that uses the updated template. This option will update the email content with the latest changes from the template. Recreating the email using the updated template would also work, but it would be more tedious and unnecessary. The template does not need to be approved before updates are reflected, but rather saved.

Test sends are not recorded on the Send Log Data Extension is the correct answer. A Send Log Data Extension is a data extension that captures information about each email send, such as subscriber key, email name, subject line, send date, etc. However, test sends are not recorded on the Send Log Data Extension, as they are not considered actual sends. Test sends are used to preview and test how your email will look for different subscribers before sending it to your target audience. The send exceeded the maximum test send threshold is not a valid reason, as there is no such limit for test sends in Marketing Cloud. A subscriber was not selected in the Subscriber Preview tab is not a valid reason either, as this option only affects how you preview your email content, not how you record your test send information. You can learn more about this in the [Email Testing Tools] module on Trailhead.

Data Filter is a tool that allows marketers to create filtered data extensions based on criteria without writing SQL queries. Data Filter can also provide a quick count of records that match the criteria before creating the filtered data extension. [Source: Trailhead]

To process the files as they are received while minimizing network, you should replace the schedule with file drop and use a filename pattern. This will allow you to trigger the automation whenever a file with a specific name pattern is dropped into the Marketing Cloud SFTP

If you want to ensure the exclusion is updated before the audience query runs, you should place the audience SQL Query Activity in a step after the exclusion SQL Query Activity. This way, the exclusion query will run first and update the data extension with the subscribers who should be excluded from the send. Then, the audience query will run and pull the subscribers who meet the criteria for the send, excluding those who were filtered out by the previous query. Placing a wait step between them or placing them in the same step will not guarantee that they will run in the correct order. You can learn more about this in the [Automation Studio Basics] module on Trailhead.