Day 2:
Figured out how to get text on the cards!
I don't know if this is the ideal way, but I'll explain how I did it in case anyone is trying to do something similar in Godot: Create a Viewport, with a Label as it's child. Then create a MeshInstance, and add a quad as the mesh. Next, create a SpatialMaterial for the mesh, pick "Local to Scene" and "Transparent" for the mesh, then create a Viewport texture for it. Enable "Transparent" and "V Flip" on the viewport. Mind that if you click on the Label, Godot goes into 2D mode, but you can't actually see the label in 2D. You have to switch back to 3D to see what you are doing with the label.
I also created a scene for the deck. I decided to use Godot's scene tree to keep track of things instead of an array, so I'm going to put all the cards in the deck as children of the deck.