Thanks for playing!
The overflow here is the limit of Godot's BigNumber library (https://github.com/ChronoDK/GodotBigNumberClass) which is pretty big (much bigger than floating points), unfortunately the math makes the numbers grow wayyyy too fast so this is probably the best that can be done.
Balancing was a big issue and this is the best I got in the short amount of time, but there is surely more that can be done.