I've said quite a bit about Grinders versus Daemon Princes in KDA as your staple heavy support. You can find it under the comments posted to the first article. I rephrase here again. KDA has no shooting except if you opt for Grinders. That's just the way it is unless you want to pay 15/20 points to arm a herald (BS3) or the Bloodthirster (BS4) with the equivalent of a plasma pistol that doesn't overheat. I don't think these guys spend much time at the range shooting so to me I'd rather use those points for another Icon.
This army needs some shooting and that's where the Grinder comes in to the equation. I run two both with tongue and phleghm. Tongue is a 24" railgun. Phleghm is the equivalent of a battlecannon but does not count as ordnance so you can fire it and the harvester gun. I run two and stick them both in the same wave. They can protect the Blodletters and keep them out of harm's way. Two pieplates per turn adds up quickly and works wonders versus horde armies such as Tyranids and Orks. They are also able to fleet and are monsters in close combat. Even the relic blade can't pierce their armor and against lower strength MCs they night just get lucky. They hit first against Carnifexes and can beat them down if they can kill them before they swing back. Their only rear weakness is meltas and high strength MCs. You have to screen them if you want to ward off melta shots. Personally I think they are much more effective versus daemon princes and the Khornate daemon prince doesn't have much going for it versus the others which have no real place in a KDA. Tongue is excellent versus rhinos and chimeras... It's very important to crack them open early and exposed their passengers.
Bloodletters are your only real choice. If they go to ground in cover that's a 3+ save... Coupled with T4 they are as hard to eliminate as your Space Marine. You'll need at least 3 big blocks and one unit should have an icon. I've taken out big squads of termies with them on the charge so they are okay in close combat as well.
Flesh Hounds.... A fast attack unit, not worth the points to me at all... I'd much rather have
more Bkoodletters to be honest.