Very cool concept. I think this could be very fun if you improve the rng a bit. It feels rewarding when you keep track of what's going on and you spend you resources where it counts, but often you're dealt a bad hand and there was no way of defending against the approaching horde.
If you plan to keep working on this, I would maybe also change the UI a bit. I would not have my UI also be a game object. Maybe you can have a dice at the head of your skill bar, or have the roll button at the bottom and replace it with skills after each roll and than have those arrows attack something more tangible.