i don't think you have to stick to their suggestion either,but the bubbles would be nice if you feel like doing the extra work. i would have only a few bubbles, large, and maybe layered. think of a bubble within a bubble, but with one edge touching. cut out some paper circles and color them in to see how they would look and scatter them on the top. i think you only need three. odd numbers look nicer than even numbers. in other words, fewer ones, but more interesting than the ones they suggest. experiment outside the box. whatever you decide, it will be great work. please show us the finished project.