Question on the two different subscriptions

[XenabelleS]

Reasons for 2nd+ character

The main story is slightly different at the beginning for each city.
Extra retainers.
Levelling one character will pretty much wipe out all the post 20 quests so unless you want to Fate grind with 9 classes, starting a new one can be easier.

[Kitya]

Levelling one character will pretty much wipe out all the post 20 quests so unless you want to Fate grind with 9 classes, starting a new one can be easier.

While this is true, because of jobs, doing it all on one character is still more efficient even without quests.