Treasure chest - 1 key. Once a week you get an exotic, no matter what level so if you do 28 and open no need waste keys on 32,34,35. If you open treasure chest after the first you will only get queen's weapon. The two chests at side, like planet chests when you patrol on Venus, you get the materials (etheric light, armor & weapon cores depending on level). Don't waste your treasure keys as they are not guaranteed per week.

Etheric light now priority to keep for upgrading armor. Those with dupe characters (2 of same class) have an easier time compared to us with 3 different ones but in about 1-2 weeks we'll get there eventually