1) Han removes every time limited buff. So for example removes Water Enhancement, but doesn't remove Healing tips. Han actually doesn't remove the barrier buffs, because they aren't buffs. You can consider them as if they worked this way: as long as the barrier is up, before each action you get the barrier advantage.

2) just the chance to get better rewards. In extreme mode is slightly higher than in hard mode, and so on.

3) space time matchmaking is made in a way that if you are top people you have it always easy. In bonds is fully random, in arena training too, in arena ranked you are limited to people within a certain range of level and points from you, in matsuri is level based, but the oldest queue in action gets priority.

4) people can attack you because you are red becuase you pludered. do the ninja test before plundering and you avoid the issue.

and where would be the side effect of plundering if was so if you are somebody that can't lose neither if is on auto?