Very helpful feedback, thanks!
We didn't had time to implement and algorithm so it's totally RNG, there are 38 cards in total. 21 numeric and two of each of the other types. The idea of keeping the card the player plays a bit longer on the screen is smart and we might implement. As for the roman numerals, it was because it fitted better with the art style, but yeah it might make things more difficult (the double digit applies to the numeric version, we now see that might not be clear xD).
It's great when we receive so much feedback from the players, thank you for it and for your kind worlds and support!