Wondrous tails was something that was introduced at the end of heavensward, you’ll most likely need to be able to access idyllshire before you can get access to wondrous tales.

As for your other question, there are some meta log challenges that require completion of other challenges that rewards varying amounts of gil. In general most challenges will reward you with exp, some others can reward gil, mgp, companion exp, elemental exp for eureka. It lists the rewards under the challenge itself.

The challenges reset weekly on tuesdays as well so no need to worry about completing them all. They’re really just a bonus for things you can do on a weekly basis.