I'll put this here in the event others are still checking in, so here goes:
I don't typically run the Blood Host anymore, as I just find it to be underwhelming in competitive games...yes, I'm talking to you, Possessed tax. A lack of assault vehicle options makes the Slaughtercult a real disappointment. What I find most effective with this army is straight up CAD, and I run two. I rely heavily on two units to do my heavy lifting, and oddly enough they both come from the HS slots: Maulerfiends and Skull Cannons. If you haven't used Skull Cannons en masse (I use 4), then you're missing out on a lot of fun/success. They hit like a brick against our worst matchups (Bike armies and dug in gunlines). Now I'm not saying I win every game against Tau or Eldar, but I rarely get tabled, and usually the games are close. With those Jink denying blasts dropping down fairly reliably (BS 5), you quickly cut down on the volume of shots coming back at you, and the Maulerfiends mop up the elements that are more resilient to AP5 shots. I also shoot for summoning in more Skull Cannons as often as I'm able (I rarely spend BT points on anything else). The best part of a Skull Cannon (beyond the obvious assault grenade effect/decent shooting power) is it's ability to grind up infantry in the assault phase. Very few other artillery units can do this, and it will really throw your opponent off guard when you charge with them. So in an army that needs to be moving forward, they compliment that role nicely.
Now I don't typically run allies, as I like to maximize the BT buildup, but the new CoTW supplement has some very tasty options in it...namely the Gorethunder battery. That formation does indeed deliver on the tabletop, but its a one-and-done gimmick, as your opponent will focus in on it and aim to get a shaken result if nothing else. So this is what I do with my KDK army, hopefully it helps, or gives you something to think about. Cheers!