•What is the meaning of numbers on the box?

and 1-7, what's the difference?

+1, i want to know it too 

 

that is just loot tier level, higher = better loots, but make sure you do want items on loot list

Chest number follows loot level. High loot level means overall better quality of loot.

 

The below gear drop list is showing what other special items it can drop on this map with separate % chance. Meaning high loot level does not mean higher drop rate.

 

This is my understanding.