Yes, you can email your content to your Kindle cloud and it will sync with most Kindle devices/apps (does not sync with the Kindle desktop apps).
The only Kindle currently to have "buttons" would be the Voyage with the haptic sensor buttons. The last one to have physical buttons would be the basic Kindle that was replaced in October 2014 with the basic touch Kindle (you can tap, you don't have tp swipe). It's often called a
K4 or K4NT (non-touch). There was a silver model that first came out in 2011 and then the next year a black model (same hardware, but with a black housing [some feel the screen on the black is a bit better too]) which they sold from 2012 to 2014.
As for an Android eInk device that will last longer than the Onyx, no one can say. Many peoples T68's are still working fine and any electronic device can suffer a failure at any point in it's life. It's always unfortunate when your the one who gets the device that fails early in its life, but I haven't seen anything specific about Onyx devices failing early for large numbers of their users (not that we necessarily have huge numbers of users here on MR).