Regarding the Field and Repudiate combo, it does work! It actually sneaks by the hexproof because hexproof only protects your permanents from spells your opponent's cast, directed at them. For example, you can also cast
Shock on a hexproof creature you control with no issue (if the mood were to strike you).
Regarding
Bioessence Hydra, I think it could definitely see play here. Especially because our Kiora starts with 7 loyalty. Unfortunately though we're only running Kiora at the moment, so
Bioessence Hydra would be a dead(ish) draw without her in play.
I don't think that's grounds for dismissing the card though, anything that gets pumped up twice by a single proliferate is good news, and it would be a decent secondary Replicate target since it would get counters from Kiora. Other hydras in the deck do not get the benefit of transitioning +1/+1 counters; it's a solid option to consider!