Cant see whether external storage aswell, as that would be good to get books from other places possibly - so not fully tied in with amazon.
You can side-load books using Calibre.
Don't think there's any options with external storage, and the newer Kindle you link to there, doesn't have as much storage as the Kindle keyboard it replaced.
I see the picture with the light, are they not backlit so much?
Don't know about the very latest from Kindle, but the model you're linking to, and the keyboard one aren't backlit.
Very readable compared with other types of screens, though. Whereas my tablet screen may not be much use in bright sun, my Kindle is and is completely readable. I tend to use the Kindle app on my tablet in the dark, though, as it's already backlit, and I can use the reverse colours (ie black background, white text) using the Kindle app, and it seems to be easier on the eyes, with less glare, in the dark.