For Story Stages, the Shop Currency reward is based off of the Stage's defined difficulty, not the LP cost or actual note map difficulty. As such, Story Stages with different LP costs may drop the same amount of Shop Currency. The most optimal ones - 9LP Story Stages with Advanced currency drops - are 1-1, 1-2, 1-7, 20-5 Normal and 20-10 Normal.

The easiest way to check which defined difficulty a Story Stage has is to enter the Guest/Formation Selection and check the background shown there - Beginner Story Stages have the simple School stage as the background, Intermediate difficulty Stages will have the big School stage with the half-circle screen, and all other backgrounds showing special stages mean the Story Stage has Advanced as its defined difficulty.

The Featured Member Bonus stacks with the Gacha/Event Unit Bonuses. Unit Bonuses apply to Event Points for Story Events, and to Shop Currency Drops for Exchange Events.

Note that the bonus from Booster Items in Story Events only applies to the Base Event Points, not the Event Points from the Unit Bonuses.