Looking at the proportions, the Nutball looks like it isn't as forgiving as a purpose built trainer. A beginner generally needs a model that corrects itself to upright flight when you release the controls. The Nutball doesn't look like it will.

Foam board should be easy to cut with a sharp knife. With most foams, you need to be careful to use glues that do not melt the foam.

Have you used a simulator? Simulators are good for orientation, even if they might not include all the variables of the real world. I just have the free version of Picasim on my Android phone but it is available for other platforms too.