Gear questions

[Naberrie]

Durability drops when you die, but it's nowhere near 50%. It is a small amount, but I don't know the exact amount.

You can save unused gear for leveling alternate classes. Most stuff that is below level 20-ish isn't worth keeping around solely to Spiritbond, so if you don't have a class that can use it just sell it.

You can't sell it if you've used it. It's bonded to you. Your options are to convert it to materia (if you've reached the point in the story where you learn that), dropping it, or putting it on a retainer in case they add new classes.