You'll need stratagems for rerolls (damage of Dark lances, or Reapers shots if you play them), and deepstriking.
Considering you can only spend 1 CP per shooting phase on a reroll, having 3-4 dedicated to that is enough.
So 5-6 is enough for Dark Eldar ATM. Moral auto-pass doesn't concern you if you don't play beastspam, and counteroffensive is situationnal and VERY expensive (it can be deadly, though).
So basically, spend the points on your DS, then use the rest to optimize your DL damage rolls.