Regarding the blanks in your hand - my impression is that they are too punishing right now. I already suffered damage from the boss and now my deck has extra "ballast" - I have no options how to overcome this challenge - it is the type of frustration that doesn't make the game more enjoyable.
If you copy the rule "paths can only connect to paths" and it becomes "blank cards can only connect to the blank edge of other cards", it would be more consistent overall. It will allow playing all cards in your hand instead of having some cards that are stuck in your hand forever