Raiders are great transports, especially for Grotesques, Incubi and Medusaes.
However, for everything else I'd take Venoms. Venoms are our main delivery system for poison shots and have a big threat range. You seriously need more Venoms, much, much more.
Kabalites are always good to have as a troop choice (or at least not as bad as our alternatives), but they are generelly preferred as semi-tax for Venoms.
With the Succubus and Lhamean you got some solid HQs, but you might also want to check out Medusaes. The Archon really isn't worth it.
I also think those 10 Scourges are a very solid number and along with Haywire Blasters (HWB in short) they are our monst reliable AT. But you also might want to test out the Heat Lances.
If you want to stay pure DE, I really recommend an "anchor" type of unit from the Covens, either Grotesques or Taloi. However, Grotesques are normally preferred because they can be transported around with Raiders and because how awesome the Grotesquerie formation is.
Since you already have a Cronos, you might consider a Dark Artisan formation (outside of that the Cronos is no good and best to be converted to a Talos).
I also think your Incubi are very useful if taken in a small squad (3-4 Incubi) and with a Klaivex the Rampage can make a huge difference. Use them as a scalpel unit to deal with something you want dead very badly and isn't too melee focused.
If you want to go for Reavers, you should consider AT LEAST bringing 6+ of them, so 12 of them sounds like a really solid number. They die far too easily and really need a certain bodycount.
Ravagers are okayish as anti-tank, but I think they really shine with Disintegrator Cannons. They compltely annihilate groups of TEQ and MEQ and even deal with AV10 fairly reliably.
Mandrakes are "okay" as well, they have the advantage of being dirt cheap and normally being ignored by your enemy. You can grab objectives with them. But if you already got some auxilliar units like Incubi or Medusae I think you should get more Venoms or Reavers instead.