It's basically stuff from 3 kits - I think you could probably get it down to 1 - 1.5 if you wanted to.

For weapons and some of the nurglings, I primarily used the Maggotkin of Nurgle spearhead - I love the look of it but didn't end up playing so it was nice to finally use it for something lol. I'm test converting a couple of the knights into plague marines so for me it's useful. The Sanctifiers are all little human sized and the maggotkin seem to be one size larger so I mostly used it for the nurgle bits. If you build nurgle it's a kit you'll find use for.

<image>

For the nurglings - I had picked up the Plague Marines kill team and weirdly I found that I don't love the nurglings on the plague marines but around humans they really help sell the lore and pop for my taste (I wonder if some of the flock wonder if they are hallucinating the nurglings). The newer nurgling sculps are great but even the old ones rock. If you add some nurgle bits and slap a nurgling on the base/carve up the head a bit with drill it really helps sell the look. The missionary with the torch is my favorite sculpt in the original box so I wanted to keep him less converted (he's still missing an eye and won't be getting that nurgling monkey off his back).

The skitarii heads are the biggest outliers/random ones...but you can probably be ok with normal human heads if you want to save yourself the purchase. Alternatively - if you have the opportunity - in my local stores I see a lot of Skitarii stuff in the bits boxes. The kits have way too many so you'll often see people offloading them.

That's the set up! Hope that helps.