Do I need to create an account in Amazon S3?

Yes, you can do it with this link https://aws.amazon.com/s3/

What does it cost to store the files in Amazon S3?

You can check the prices in this link https://aws.amazon.com/s3/pricing/

How long will I receive support when I purchase this plugin? And what happens after?

After one year you’ll still be able to use the plugin you have downloaded and installed as is, no premium features will be cut off or affected by the license expiration. Yet, you will no longer have access to support and updates.
On the other side, if you want to renew support and updates, you can consider that renewing before the license expires entitles you to a 50% off discount! 🙂

If you add an image to the media library will the created thumbnails also be sent to the S3 bucket? When a customer purchases a downloadable product, does the customer see the site domain URL or the S3 URL? In other words, does the plugin pull the S3 file and then deliver it to the customer via a site domain URL….or is sent directly from S3?

When adding an image to the media library and the checkbox Copy also to S3 is checked, all the created thumbnails will be sent to S3. This image will be served by S3 for any size. When customers purchase a downloadable product they can see an S3 link. By uploading the files to S3 as private (recommended) this link will be temporary. The purpose of the plugin is to serve the website files to improve the site speed. About downloadable products, the temporary links served by S3 add a security step.