I've not made anything with isosceles triangles. What ever you are piecing, the two things to watch most closely is the cutting and sewing the 1/4" seam. Watch that your ruler doesn't slip. If it does, get something to stop it (those sandpaper dots or Invisigrip). I can't help with the 1/4 in seam. I'm on my 7th quilt and still have trouble with it.
Good luck on your project.
bkay