My Stone economy with Kirai is quite simple: I need three or less stones per game for summons. This accounts for the fact that with your starting hand + whisper you often see the right card on hand (9+ crows - as Drowned is already a great summon). Any extra stones goes for protecting Kirai or Vendetta in case I over-expose myself. I play Kirai quite aggressively I must say and I'm not afraid to lose her on turn 4 if my opponent overexposes or wastes actions to get her.
A bonus action from Killer Instinct will give me another stone or two on occasion.
So overall I'm fully ok to start a game with only 3 stones.