Hi, I am not experienced enough to make this one. But I recently went to the 3 day "Sewing with Nancy" when she talked about this. For the circle in the middle, she had a really clever hint: sew interfacing to the circle, turn it inside out (I would recommend clipping along so it lay down flat). And then trim the middle of the interfacing out carefully so it's not so bulky. Now the circle is nicely finished, all you have to do is applique in on top of your form. Hope this is understandable.
I actually do it when I make interfacing for clothes as well.
Thuan