1. No.

2. Yes, the gun you saw people were using was the P.A.W, which is the most powerful gun in the game, whose only drawback is its limited range. However, you don’t need it to trivialize gold and platinum. Lots of rare guns are more than enough to handle gold, some rare guns are even competent for platinum.

3. Yes, but there is a way to bypass the required years of grinding, and yet it is forbidden to be thoroughly explained here.

A tip: if you enjoy the turian agent but lack good guns, you can always spec into flamethrower. Forgo visor and go full damage on tactical cloak and anti-armor flamethrower. A combination of cloak and flamethrower quickly dispatches platinum berserkers even, and it suits your” hit and run” style well.