1. The eyes Kazui summoned were Yhwach's eyes. Curious what that means.
2. The opening bit about the fish is referring to Ukitake, and may have been spoken by him. And Sōgyo no Kotowari translate to Truth of Pisces. The twin fishes. (this last part taken from Reddit)
3. I wonder if Burn the Witch and Bleach will cross over in this, since they are in the same universe. Would be an interesting thought.
Regardless, it seems Ukitake will be center to this, which I'm 100% all for. I do wonder if Kubo will use this to bring back some of the captains. I'm still bummed we never got to see a full rage mode Retsu.