Hey there!
1 & 2 are both mentioned in the rules- the game's over when either all your friends are out of energy, when you run out of energy, or whenever you want to stop playing. When a Friend runs out of energy, you remove them from the game and shuffle their cards into the other stacks.
For 3, it's an effect thing, an emotional whosawhatsit. If you draw the marked card again, just mark it more.