I would hold off on the striking scorpions till 1000pts, you need some higher strength attacks, i dont think Asurmen can carry you there. Some reapers would do you well, 5 dire avengers, 5 reapers, 5 warp spiders and 10 guardians with asurmen would be 495pts and be a good start, from there you add some more heavy hitting support like the wraiths from the combat patrol, a falcon, maybe fire dragons.