I'm using an S7 edge and it's on the default 1080p resolution. It's not blurry at all. The difference in quality between this screen and the screen on S3 is very noticeable. The non removable battery is the only downgrade I see. Everything else is a huge leap forward. Even battery life is much much better. You likely would not need an external battery.
I'd have to see it for myself. My 4k laptop makes me gouge my eyes out in 1080p mode.
As for the battery life you mention, that's probably just the Android upgrade. I've easily doubled my battery life in 3 major Android version upgrades. 10-15 days (depending on usage) is normal now with a 7000mAh battery.
