Post EW, I still have Questions

[MikkoAkure]

1. How did Emet and Lahabrea avoid being sundered?
1a. How is Elisibus unsundered when he's the heart of Zodiark and Zodiark is sundered???

We haven't learned why the unsundered are unsundered yet, but Elidibus was spat out of Zodiark before the Sundering. There was a good deal of time from the 2nd act of Zodiark to the Sundering. We don't know how much time, but it was at the very least enough for the Ancients to have their first big disagreement ever, Elidibus to eject himself to mediate, and Venat to gather her supporters and summon Hydaelyn.

2. Where was Azem during the Final Days and what were they doing?

No one knows yet.

4. If tempering is an add-on to primal summoning and not an unavoidable requirement, then who included it in Zodiark's summoning and why?

Part of tempering is the shift in your aether towards a certain element. It wasn't specifically built into Zodiark, but he is so powerful and aetherically dense that his summoning shifting the aether to those present to darkness was unavoidable. The degree to which they're tempered is debatable because of the fact they're Ancients and it wasn't intentional, but the Ascians still spent 12000 years praying to their "one true god" and talking about plunging the world into darkness etc. so it at least had some effect and thousands of years of doing this didn't help their mental state.

6. And this might just be me, but why isn't Azem a proper character in their own right like Ardert, instead of being somehow determined by our CC choices in the future?

I feel like Azem is closer to "us" specifically than Ardbert is. That's also why Azem's gender changes depending on your character. Plus Ardbert was created all the way back in Heavensward before they had even planned for Shadowbringers so him being the First's part of our soul was probably a retcon behind the scenes. From what was said during a Fan Fest, it seems that a lot of the writing isn't planned too far away and they leave just enough open threads for possible future plotlines. But now we'll probably never see Azem in person since they look like your character only if you play Hyur. It would be especially difficult to reconcile if you're a lalafell or hrothgar.