Hey thank you so much, i'm glad you like it!! Using it in a Fabula Ultima campaign is such a cool use case I'd love to hear about how it goes!
As for online implementation, I usually use playingcards dot io as that's the best (and free) way to do cards online that i know of. I've not done any automation for it though, so usually when the threshold is crossed the players will just manually select and exchange cards. Hope this helps!