– The first one is a WordPress issue, should be fixed in the upcoming WordPress versions
https://core.trac.wordpress.org/ticket/47510
– Make sure all pages have featured images set, so that the thumbnail in the sidebar doesn’t have default blue image, it is the one that doesn’t have height and width and causing the warning. We will include its height and width in the next version release.
Images should be bigger than 658 x 300 px otherwise theme won’t be able to generate proper images for slider, thumbnails etc causing blank space issue.