I am making the wasc cake and my first "Big" cake.I have never made anything bigger then a 10" so I need to know if I need to put a heating core in the middle. Also I only have only "1", so could I use my over size flower nail for the other 12" ? Thank you

Flower nails work very well. I use them all the time. When the cakes get big, I use more... Just make sure that they are greased too..

For more than 20 years I have baked up to 16" cakes w/o any kind of heating core - not even a flower nail.