Is LS you lose one health, is that mechanic carried over?
Nightshade is the only Hero in LS that takes damage from playing Death cards. It's not a core mechanic baked into the game, just her downside for having Superiority in Poison and Shadow. (And if played well its not really much of a downside)
I played death at Warhammer fest and didn't notice anything like this, so don't think so
No, closest there are to that are a Chaos unit (Bezerkers or something)? That would sometimes damage you instead of the opponent
You don't lose health for playing cards unless the card specifically states you will lose health when playing it.
There might be a spell or unit that will cause self damage but that will be a payment to do something since there are vampire units and champions so there are "drain" type of abilities and spells most likely in the game. So I wouldn't be shocked if there will be a a card or two that does self damage in the Death Order along with Chaos Order following Khorne units.
Eventually this might be a mechanic that add into future expansions.
I wonder if this sort of mechanic will make it's way into future expansions.