If a creature affected by the Pirate token can't attack for any reason (such as being tapped or having come under that player's control that turn), then it doesn't attack. If there's a cost associated with having it attack, the player isn't forced to pay that cost, so it doesn't have to attack in that case either.

To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases (such as that of Pursued Whale), then apply any cost reductions. The mana value of the spell remains unchanged, no matter what the total cost to cast it was.