3.
When the returnd status is "Done", or the progress is "100", you get an URL for the grid of 4 preview images, from the uri field in the response.
4.
You also get a list of valid buttons action in the response, you can use them to do subsequent actions, such as regenerate another 4 images (e.g. "🔄"), uspcale the selected image (e.g. "U1"), or regenerate another 4 images based on the selected image (e.g. "V1").