If multiple replacement effects are applied to the same permanent, that permanent's controller decides the order that they apply. in particular that means you can apply General Takaki's ability before any abilities that add or double damage apply.
General Takaki's ability works unintuitively with trample. Lethal damage is determined by the amount of damage a creature assigns (usually with its power) and not the amount of damage it will deal due to replacement effects. If you attack with a 1/1 trampler it will deal 3 damage to its blocker and no damage to the defending player.