Hi,
sorry for asking this as I don't wand to cause any work but I think it is quite important and was not answered fully in the documentation.
I want to optimize the images so loading does not take so long on mobile.

1. When uploading an image to a portfolio it is stated that "Recommended image width is minimum 1600px wide".
If I have retina x2 does this mean I should upload 1600 or 1600*2=3200?
2. I heard that WordPress optimizes image quality and creates several sizes for the different usages (thumbnail…). Is this correct? Does this mean I can Upload high quality 3000×2000 images and WordPress does the rest?
3. There are plugins like https://wordpress.org/plugins/imsanity/ or https://wordpress.org/plugins/ewww-image-optimizer/ which create smaller files and do this even automatically. Do you think that makes sense?

Thank you very much,
Uli