Is there a way to find the amount of space an element should take before rendering?

There's some functions on the TextElement to pre-measure text but nothing "general" for pre-calculating the size of an element. My recommendation is to let the element size itself, detect the completion of the layout by listening for the GeometryChangeEvent, and then reading the final size from element.resolvedStyles.width/height. If you must, you can do this off-screen so the user doesn't see any popping.