Temple of Meraveran gives Melee +1. Thus the creature will only get the extra die on the first attack of the action as per the regular Melee +x rules.
I don't think that's the part he's talking about.
I think it would get 3 valor if your creature suffers damage from all 3 swings of a triple-strike. But I'm pretty much guessing, and my guesses are often wrong. Would love to hear an official answer.
Ah, I am sorry I misunderstood! Yes, it says "when a creature you control is attacked and damaged by an enemy creature..." Which would indicate every time with no limit. So a hydra triple striking, a counterstrike, a zone attack, a sweeping or double strike would all grant as many tokens as there are attacks made against creatures you control. This is slightly different than "Friendly creatures" so in a team game you would not get tokens for your ally's creatures being attacked--only your own.