Haha, I know what you mean about the breading aspect being number1. Suggestions of a planted display tank designed around the fish seem to get an intrigued response every time, I would've thought it would be old hat with these fish
As far as tank volume, I see the suggestion everywhere that they're happy with small spaces "like bettas", which I don't entirely agree with if we're getting under 5 or 10gl. But the defense is always that they live in small uncirculated puddles.
Then there's the "jumping out of shear exhilaration" and the need for a tight lid. I've read some killies were observed jumping from puddle to puddle in the wild, possibly in search of food. From what I read about male enthusiasm and what you mentioned about relentless chasing, I wouldn't be surprised if males were jumping puddles in search of mate as well. We have killies here in FL that climb into emergent mangrove roots and live there for months out of water. This point of jumping behavior etc and why it's happening totally changes the entire "required volume" debate. You enter the realm of animal intelligence and ethics, and start talking about animals like the octupus.
I think most of us dedicated planted and reef folks are looking for harmony in our tanks over anything, at least I hope most have figured that out because it's all tied into the artistic visual and the moods that we're after while we constantly push ourselves into deeper territory in this hobby.