And the last questions about this topic, because I’m struggling with this for some time: can you suggest a size that I should use for the featured images?
In the mean team I read several articles and I think the max dimension of 1200px for landscape and 1200px for portrait format should be good enough.
I’m using already the plugins Shortpixel and Perfect images (previously called WP Retina 2X). In Shortpixel I specified a max of 1200px.
And what should I do with the configration in WordPress > Settings > Media? Just leave them as is?