1- It does sometimes, very small ratio tho.
2- depends on the skill level, magic power, and banner level too.
3- It will give you a weapon needed for rare craft job.
4- 5k+ def is cool in lab run. In dungs, actually I don't advice to go max def since your attack stats will be reduced. Go KW or Burning Rage in dungs. for dmg, get +7 weapon n you will be fine. Get them good accessories too.
5- yes ofc, in pvp, arena, and wars.
6- for lab tank get Golden Dawn boots and armor with mace set up, u can go HE in gloves and helm. For dungs, go KW. Try keeping some resi too. For pvp, go arena set.
7- Goodluck