Since I built my Khorne Demon army I've only made one addition to the army and that was a unit of OOP Blood Letters, the old beefed up metal models. I've had this model setting on my desk for a quite a long time.
The ole Belakor model. I thought it would look pretty cool in the army and have wanted to paint it for quite some time. So I think it will make a cool addition. I did not do any conversion work on it. My old army is all mounted on smooth faux blood pool bases. To prep the base, I sanded and shaved all of the relief off it.
Back when I built the army, I used pieces of cut up plasti-card for the bits of land, covered in HO Scale railroad ballast. I had also added heads and demonic looking hands in the blood pools.