That is going to be a beautiful quilt. You might try this site to calculate yardage:
http://www.vrya.net/quilt/flash/QuiltCalc_Loader.html
I used it for the Thinking Outside the Block design I am doing & found it very easy to use. Basically numbered my fabrics, figured number of each size of each shape & plugged it in. Print out the results for each & you have the cutting layout too.
Let me know if you need help. Could play with it one evening at home.