Hmm, I can certainly start brainstorming some stuff, but I just found this and it seems rather fascinating in concept.

EDIT 1: As for group/unit names, a grandiose option could fall along something like "The Order of Grey Keep", or if we are thinking something more militaristic, The Royal Regiment XXIV, cue some fancy nickname for them, Dark Stalkers or Dawn Bringers, just some idle thoughts so far.

I'm thinking a castle suspended by Lumien magic, literal pillars of light holding up a grand keep that the shadows couldn't reach readily, and the same pillars of light providing methods of getting up and down from the keep. Just a brief thought I wanted to get thrown up.