Re: How scratch resistance is the screen
Gorilla Glass is about 6.7 hardness (where talc is 1 and diamond is 10). A tempered glass cover is about the same hardness.
I find that a cheap 3.$5 plastic protector is all a phone needs. It'll take the scratches, it's cheap (with 2 phones, after 22 months, I still have one unused one left), and most of them are pretty thin and pretty transparent. (If you "wipe" the screen with the sticky side of tape to get every last dust particle off before you put the screen protector on, you shouldn't notice the protector. One tiny dust particle can make a large bubble.)
Tempered glass isn't going to protect the screen from a direct drop - it just won't spider like the screen, it'll crumble, but the screen will still crack. A good case with a silicone rubber lip protruding past the screen (like an Otterbox or even a cheap TPU case) will do that.