I've made one billowing cake and I used a 50/50 mix. I find you can't really do them in advance as it doesn't allow you to fill in between the layers properly once they are dry. I add one billow and then depending on what I'm using in between each billow (brooch, candy, etc) I use that to press into the billow as a guide so I know exactly how the next billow will fit. It worked for me. Here's the link to my billowed cake so you can see what I mean. I hope this helps....