One of the best bangs for your buck when getting into either Thousand Sons or Disciples of Tzeentch is to pick up the Changecult box. In either game, Acolytes are pretty worthless, so let's make them into Tzaangor with a super easy conversion.
The Tzaangor sprues come with a TON of extra heads. This makes for easy Tzaangor conversions. I like the idea that some Tzaangor are mostly human still, so all I do is just add the head. It will take you a tiny piece of pinning material (I use a little piece of paper clip) and a tiny ball of green stuff.
So to add this head, I just drilled a hole in the head and in the neck, then ran that pin through a tiny ball of green stuff and plugged the two models together. If you'd like more pictures, I can add a better tutorial, just let me know.
Here are some regular Tzaangor mixed in with Acolyte Tzaangor. They work pretty well together. I'd say the only thing I would watch is how you arm your Tzaangor. The Acolytes will have a lot of shield arms, so I would plan for them to be the shield bearers in your army if you are building for AOS.
Let me know what you think.