What should my self-balancing robot's weight be?

I'm designing a self-balancing robot and was wondering what calculations I need to make to determine how much my robot will need to weigh. I was considering using https://www.pololu.com/product/4751 as the wheel motors, but I don't know at what weight it'll be able to balance efficiently and at what weight it won't. My robot should be able to carry an object with a max weight of 450-500g, but I can lower that requirement if needed.