Figure how how many rows vertical and horizontal you can get out of 104 - 5 inchers (remembering the 1/4" seam. I would have an absolute ball with this one! Actually I am making a Floating Star quilt right now and have to cut out over 800 2-11/2x2-1/2 squares for half-squares. I'm loving it. What, also, is a lot of fun (unless you have a dog that has a fetish for quilts, done or not) is to lay the squares on the floor and just look at them and then decide how you want to place them, etc.
Preparation is 90% of the fun! Edie