I use eos whenever I know that the party won't be taking large amounts of damage, or if I'm playing with a skilled or overgeared whm that I trust to patch up the raid. Think of Selene as a 10% buff to the party's damage. Managing her cooldowns takes a bit of practice, but once you r got it down, a solid party will appreciate the damage boost.

In regards to stress, it's the nature of the beast. Try to keep a healing priority for when things get messy. Do your best to follow it and don't panic. Not healing at all is worse than sloppy healing. The hardest fights for me to keep focused in are fights that I don't know well yet. With practice, you learn to anticipate moves with adloquium/succor, and the strain becomes less for everyone. Keep at it, and you should find your groove for each fight.

And a quick tip for those brayflox speed runs, don't be afraid to spam adloquium, especially on the first pull. You'll need to be a bit cautious of the mp drain, but energy drain and aetherflow management make it a breeze. Scholar performs best by maintaining the tanks hp, compared to whm that excels at replenishing the tanks hp. It's a subtle nuance, but it's an important one.