Ok, talking it out while I type. For those that have already had their coffee, correct me if I counted or multiplied wrong.
So with one WoF, you should get 4 9" blocks, plus a pretty good hunk of scrap. Very unlikely to get 5 blocks, most fabrics I figure with a usable 40-42" width. It will take 2 blocks to make the 4 triangles so you will get 2 blocks per WoF.
As Tranum said, watch the spin! Always cut from the same side of the fabric in the same direction. I just did a project and had I folded the fabric I would have gotten half the pieces unusable for my design. I write myself a big note on a full piece of typing paper with a diagram and something like "right side white on top, cut left to right" in big letters.
Ok, so there is no one set size for a quilt. I'm usually aiming for about 100 inches in length, and about 80+ inches in width for a queen sized.
6x7 12" blocks is a pretty good place to start. That would make it 72x84 without sashing or a border. Add 14" for 2" sashing across, for 86" wide. 16" for the length which puts you right at 100". You can use less blocks and wider sashing or add a border as well.
6x7 = 42, and you get two blocks per WoF, so you need 21 WoF rows, or 105" which would be 3 yards (108") of each fabric if you use only two fabrics -- note: That does not include the sashing. And that works out exactly to the 6-12 yards that I expect to use to make a queen sized quilt!
Otherwise, you should be able to get the two blocks out of a fat quarter (watching your cutting).