Great show! Makes you really invested in the story and characters.
I still have a few unanswered questions though:
- How did time travel start if it was a consequence of the plague which happened due to time travel? Katarina ended up inventing a working time travel solution due to the plague happening in order to prevent it. But the plague happened because time travel was invented and the witness was able to orchestrate the whole thing.
- Why did the messengers have to travel back in time using Katarina's machine if the witness had access to time travel himself?
- Why the house of cedar and pine is used by Olivia? Olivia being the witness doesn't make much sense with the house of cedar and pine as this place was not significant to her as it was to Athan.
- Was Athan the witness originally but because he was saved by his parents then Olivia became the witness, or the witness was Olivia all along? If she was the witness all along what is the deal with Athan being treated as the witness by the 12 monkeys?
Cole is the start point. For Cole to exist, time travel had to exist. That's why "deleting" Cole fixes everything; without him, none of the rest happens. The plague is just part of how time got time travel to exist.
The Messengers had a stealth mission to do; you can't just drop a small time travelling city into place to drop them off. And they only had the four vests, so no using those for the Messengers.
It's used because it's what "young Olivia" expected the Witness to use. Olivia only becomes the Witness along the route of believing that Athan was the true Witness for most of her life. So when Old Olivia has so communicate back to her younger self, she has to maintain that assumption.
Athan was always the "first Witness", but never the second (the one with the mask in Titan). Again, the path to Olivia becoming the Witness required her to believe the Witness was someone else, so that's a fully locked circle of fate.