Thanks for answering Jan, spot on!
I’ll answer the remain questions (I work for @deliciousbrains)…
3. What happens when all media files are permanently moved to Amazon and my client decides to leave my services? How do I reinstate all their images back to WordPress?
If you haven’t used the “Remove Files From Server” option then there’s nothing to worry about, they have all the files locally.
The Pro version has a tool for downloading the files from S3 back to the server (if you’ve removed them from the server), it also has a tool for downloading to the server and then removing from S3 should you want to do that.
You should really be setting up S3 for the client anyway and using AWS keys that they control as it’s their data. Although I can understand if you’re providing a full server hosting package that this might not be ideal.
4. Many websites have an image compression plugin like WPSmush. Is there a way to delay the actions of WP Offload S3 Lite by 1 minute? The idea is, the images get compressed first, then WP Offload S3 Lite moves the images to Amazon.
In most cases what happens is the image compression plugin takes precedence in the filtering of the postmeta data (which WP Offload S3 uses to trigger its upload) and does its compression and rewrite of postmeta before WP Offload S3 then uploads the newly compressed files. However, some plugins such as EWWW Image Optimizer are telling WP Offload S3 to not upload to S3 (there’s a filter for that), doing their work in the background, then updating the postmeta which triggers WP Offload S3 to upload to S3.