1. Conditions can only apply once, but if you like them stacking, you can do that too.
2. You can always heal back to full health on a good nights rest or spending time with your friends. Rest and Relaxation is mainly to remove any conditions that you have. On a 6 or lower, you will not remove any conditions, break that relationship, but still heal back your full HP.
2. The person who called the attack makes the roll. Your comfort with meta gaming may allow the person with the highest emotional rating to make the roll. But I always let the person called the team attack make the roll. And they can always spend more power points than needed to gain advantage on that roll. So if there are 4 players, the need 5 power points among them to make the team attack. If they spend 6, the person making the roll has advantage on that roll.