What is the transaction limit on the number of "sendEmail" method calls?

A developer is writing a Visualforce page to display a list of all of the checkbox fields found on a custom object.
What is the recommended mechanism the developer should use to accomplish this?

What is the transaction limit for the number of records using QueryLocator?

An Apex Trigger creates a Contract record every time an Opportunity record is marked as Closed and Won. This trigger is working great, except (due to a recent acquisition) historical Opportunity records need to be loaded into the Salesforce instance. When a test batch of records are loaded, the Apex Trigger creates Contract records. A developer is tasked with preventing Contract records from being created when mass loading the Opportunities, but the daily users still need to have the Contract records created. What is the most extendable way to update the Apex Trigger to accomplish this?

Which technique can run logic when an Aura Component is loaded?