Wondrous Tales always give about a half level's worth of XP when turned in, on top of any rewards you might get from randomly filling in the sticker book aspect. I tend to turn them in on jobs that are more hassle to level up, like healer or tank.
Once you have any jcombat obs at the current level cap, Khloe gives you the hard mode books, where most of the tasks are things you cannot possibly solo, but the rewards include more endgame grind stuff like the latest type of high end tomestone (Aesthetics, for instance, right now). I've been very carefully keeping the characters still working on Dawntrail below L100 on anything, rotating what jobs I use for MSQ, etc. Eventually the MSQ is L100 and I'll lose access to the "run through all nine entries in half an hour" trick.
Khloe's big sister Zhloe Aliapoh is one of the Custom Deliveries people. Their big sister Qih coordinates the Studium Quests in Old Sharlayan (that info is not available in-game, it wasn't confirmed until the relevant volume of the Encyclopedia Eorzea came out). The other Aliapohs in the game (Jihli from the not-Easter event and Leih from the Archer class quests) seem to be unrelated. It is a common Seeker of the Moon name.
---Dave