1. If I'm in a group and I loot a monster we all killed, am I stealing from my teammates, or do we get our own drops?
Loot is shared. The credits are split and you roll an imaginary 100 sided die to determine who gets the item. You should choose need if it's an upgrade and has the right stats for your character. If you want it for your companion, ask the group if you can need for it. If someone else needs it for their own character they likely will object. You can choose need on everything if you like, but you will see your queue times increase as people who place you on ignore will no longer be matched with you.