Need some Qs answered on a level skip

[Rongway]

he needs the story skip potion.

This is not correct. Expansion job boosts only require that you have the expansion registered. They do not require that you have advanced the story beyond the very first 2.0 quest -- that is, you only need to be introduced to your starting city and then allowed to leave the mini-city instance so you can find the postmoogle to claim your skip book.

For what reason does he want to play DRK? If its gameplay then I would recommend he pick up PLD. PLD and DRK from 1-50 are very similar, so he would be able to easily transition to DRK when he reaches Ishgard.

This. DRK is literally a reskinned PLD from 1 to 30, and there's very little to differentiate the two from 30 to 50.

It's worth mentioning that (even if he's not interested) getting a level skip for DRK will also get him Red Mage and Samurai "for free", as the only prerequisites are being Lv50 and having Stormblood installed, so those unlock quests should immediately become available.

But to be fair, any job boost will do that, since all job boosts take you immediately to 60.