Hero of Leina Tower

• WWizards of the Coast2013-09-15
  Official Ruling
  Heroic abilities will trigger only once per spell, even if that spell targets the creature with the heroic ability multiple times.
• WWizards of the Coast2013-09-15
  Official Ruling
  Heroic abilities will resolve before the spell that caused them to trigger.
• WWizards of the Coast2013-09-15
  Official Ruling
  Heroic abilities won’t trigger when a copy of a spell is created on the stack or when a spell’s targets are changed to include a creature with a heroic ability.
• WWizards of the Coast2018-12-07
  Official Ruling
  The amount to pay for is chosen as the triggered ability resolves. No player may take actions between the time you pay and the time Hero of Leina Tower has X +1/+1 counters on it.

Rulings via Scryfall