Hi,
1. This theme uses 3 images attached to a page as header images. Please edit this page, click on the featured image option and select “Uploaded to this post”. You’ll be able to re-order images attached to the current page (with drag and drop), and set 3 first images this way.
2. Yes, but this requires CSS tweks, it supports a solid color background by default.
3. They depend on the image sizes, please try uploading images in portrait format.
4. The easiest way would be re-importing this page from the demo content, but you can also re-create this layout with blocks.