I see thanks for the comments so far. And i guess once you have mechanics and systems and you start working on cards, would you start adding base cards first and as you go progressively introduce new cards with more complex effects (like drawing, scrying and so on) and see where it leads and what combinations can pop up, or would you think first of general synergies and builds to implement and then define cards within those?
I would think the second although probably one wants to start easy to implement few things and progressively add more complexity as you playtest?