To my memory, the 1.0 starshower was something that inexplicably happened after the Battle of Silvertear Skies. I don't recall anything anywhere hinting at what awakened the Echo in 2.0's generation, though I would wholly believe it was the Calamity (Dalamud / Bahamut himself).

I can't say for sure what Elidibus' plan is, but I can say with relative certainty it has something to do with disrupting society, at least in the Crystarium. I feel there's a little too much attention put on that for it to not be relevant. Other points to note are their dreams of glory (heroes act without thought of glory or reward; accolades are a consequence, not a goal) and that while Elidibus may have titled those he awoke "Warriors of Light," that title is used to denote one with Hydaelyn's blessing (in part or in full), something they do not have. Yet. (The Doylist answer for it is more likely "We need to refer to the PC in the voiced dialogue, so let's go with the classic title." Otherwise you get awkward stuff happening like in X, where nobody ever actually says Tidus' name.)

It's late so I'm not jumping on to check, but I also believe Elidibus said that we would "meet our end" at their hands, so he wants them to kill us...

Well, whatever direction this goes, it's gotta go fast, given as precedent means the next patch will be the "True End" of Shadowbringers. Please look forward to it!