The Kingdom Builder feature should work almost exactly like this website for Hearthstone (similar to how Hearthstone works in game): https://searchstone.io
Want to only see Hunter cards? Click Hunter and bam, only Hunter cards. Want only 3 mana cards? Click 3 mana and see only 3 mana cards. Want to see a cards with a specific action? Type "Deathrattle" in the search and see all the Deathrattle cards. What was that card that Hunter card that was 5 mana and had a deathrattle and had an attack between 3 and 5? Oh it was Corpse Widow.
Kingdom Builder should be exactly that.
Show me only Prosperity (this already works). Show me only 4 cost cards. Show me only Projects. Show me all cards that give +actions. Show me all cards that say "Trash This."
And add a button to randomly generate kingdoms that you can just continually press until you get one you like.