The Crystal Tower quest chain begins in Mor Dhona.
The "Light of Hope" requirement only occurs when you are in the post-ARR MSQ, so you'll want to tune into the post-ARR story until it tells you to complete this quest. specific. You'll need to be iLvL 55 to access the first wing of the Crystal Tower raid, Labyrinth of the Ancients, but the updated loot tables from quests and dungeons should allow you to overcome this barrier.
Once you have reached the quest “A Time for All Purposes” and are seated at or above iLvL 55 “The Legacy of Allag” From the Outlandish Man (X: 21,8 Y: 8,1) in Mor Dhona. This will launch the crystal tower arch, and all you have to do is follow it to reach "The Light of Hope." Cleaning the fenders won't be much of a problem - they're part of Alliance Raid roulette, which means high-level players dominate alliances. While you shouldn't ignore the mechanics entirely, you're likely going to get carried away. That said, there is no loot limit in Crystal Tower raids, so grab all the upgrades you can - they'll make later quests easier.
The story is long, but I recommend watching all the cutscenes. The story of the Crystal Tower had become a requirement for a reason. The events of this arc play a big part in the Shadowbringers expansion, so unless you're doing no shit about the story, you'll want to be careful. Once you complete the third wing, The Dark World, you will move on to “The Light of Hope,” and once that is cleared, you can resume your progress in the post-ARR MSQ. There are two quests that follow “The Light of Hope”, but they are not necessary to advance with ARR. I recommend them for the extra story, but you can skip them if you want.
