So, here’s what I have so far:
In the city, the GM draws one card per mark in the gauge you’re checking against, and picks one they like best. They interpret it and say why that’s a miss, weak hit or strong hit.
In the castle, you draw one card plus one per stat point, pick one you like best, and interpret it to say why it’s a miss, weak hit or strong hit. (If your stat is -1, draw two and the GM picks which one you use).
Advantage
You and the GM both provide an interpretation of the chosen card, and the group decides which is more appropriate bearing in mind the advantage you're working with.
Disadvantage
Same as Advantage, but the others decide with is more appropriate bearing in mind the penalty you're under.
I didn't want a system where I simply use the card as a random number generator - and hopefully if you have meaning-rich tarot cards to hand and you'd like to use them in a game you'll enjoy the prospect of interpreting them ^_^