User blog comment:DSHaseo/Getting Back in the Game, Help Needed/@comment-26399146-20150813060407/@comment-217.169.117.37-20150813105224

Grand Quest missions unlock by defeating quest areas and previous GQs. Grahdens GQ is " Unlocked after beating Lucius in  Bariura  and completing  Cobalt Spirit's Waking  (Mission 3)" as written on the wiki page.

As for most content now you will need hp and def buffers, a mitigator,a healer, a status ailments remover(Elimo 7* does all last 3).

In my opinon (don't hate if you think different) you should focus on maxing elimo first since she does the job of 3 or 4 different units then  Toutetsu  for the atk buff andwhomever else you can fit with your cost.

Good Luck ;)