Collapsing the model is really tedious work. This tutorial is really good: www.youtube.com/watch?v=DLk6Zs…, it explains and shows in-depth how to collapse the model with precreasing, which is better than other tutorials I've watched when I began making this model. Let me know if you still need help! I will try to explain.
To get them puffed up, I usually flatten the ball and then put something like an eraser on top of it. After a few days, I remove it and it kinda helps the ball to have more of a sphere shape, if that's what you mean. I also use tape to join the ends, bulge?