Destiny 2 Questions & Answers

I have obtained some of this from dismantling gear and I have no idea what it is used for. I am guessing it is like glimmer and I can buy stuff with it, but I would appreciate if anyone could explain what it is and what it is for.

Is it possible to go back and replay a mission from the main story?

If I open these now will i end up wasting the chance to get better loot in the future. If the loot you get inside is based on your current level, isnt it better to wait until you are higher before opening them?

I have reached level 20 over an hour ago and I still have not unlocked my achievement, is there a bug or what?

The aiming in Destiny 2 feels a bit off. At first it moves slow and then it goes fast. Changing the sensitivity has not fixed it and using a different controller also made no difference. 

I have obtained some legendary shards after dismantling a load of excess items in my inventory. Where can i spend them or what do they get used for?

I have been collecting a lot of glimmer from chests and dismantling gear, but I havn’t really found a need to spend it on. It isn’t like we need repair kits or healing potions etc. What are some good things to spend glimmer on?

I have reached level 20 and the trophy for this (Long and Winding Road) has not unlocked for me. Is there a glitch with this?

I have heard these mentioned a few times from higher level discussions. What are bright engrams?

What is the maximum level your character can reach in Destiny 2?