I'm running a very similar list right now, yay Thousand Sons!
Here's some thoughts:
Sorcerer - Why the disc? That means he has no one to hide behind all the time. I assume you're trying to put him in with the herald and the screamers, but considering there's a very likely chance they don't turn up until turn 2+, It might be a good idea to look at other options. Trust me, i like the idea of discs, but they kind of lose their steam when your sorcerer can get insta killed by an errant blast from a krak missile, or worse one of those pesky
GK dreads.
Kson squads - love 'em. Don't change a thing. - warpfire gargoyles on the rhino?
Cultists - I like the idea of cultists, especially in a Tzeentch army, but what exactly are they trying to do in this list? It doesn't seem like they have much of any survivability, there only being 10 of them, or much firepower for the same reason. If you're looking for a cheap unit to hold a back objective, I'd consider another squad of Pink Horrors. Warpfire is awesome.
Dreadnought - not calling it a hellbrute, not doing it. I have one, and I like that it's become a bit more useful now, but here's my issues with them: 1 - they're gak magnets. not in itself a bad thing, but chances are it's going to get blown up quickly. 2 - they move slow. Unless you're drop pod-ing it in (which chaos can't do
wtf) this guy will never make it past the half way point of the board. My recomendation on them is to: 1 - take 2 of them, and 2 - take long range guns.
Predator - A very decent heavy choice. The biggest problem with Ksons armies, is the lack of tank killing. Maybe take 2!
Herald - this guy suffers from many of the same problems that the sorcerer does (ie. the disc.) I honestly can't remember if the chariot is different from the disc, so if I'm way off, please forgive me.
On a side note, the Lord of Change/Fateweaver is a huge badass, well worth any number of points (about 300 with the right options). 1 - it's a flyer, capable of vector striking other fliers

2 - it has breath of chaos, one of the most broken weapons in the game. This is basically the only solo unit in the game that I feel OK just having 1 of.
Pink horrors - awesome. Maybe take 2.
Screamers - I like them in theory, but I think you'd be better served turning them into flamers. Breath of Chaos (which i've already talked about) is amazing. and they have warpfire. They're also a fairly adequate assault unit, provided you breath/warpfire your target first. Well worth the points!