Bear in mind that this list is intended to add towards making a more powerful build.
Sorcerer Lord (Level 4)
Mark of Tzeentch
Disc of Tzeentch
Book of Ashur
Power Familiar 405
As said, you're only allowed one Arcane Item. I think that the Book of Ashur is fine as needed - take instead the Golden Eye of Tzeentch to protect it from Magic Missiles (3++ Ward Save). As you shouldn't really be going into combat, other than to take on War Machines etc.
Personally, I'd mount him on a Disc - a 3+/3++ Save is not to be sniffed at.
Exhalted Champion
Shield
Mark of Tzeentch
Sword of Swift Slaying
Dawnstone 175
If this character is intended to be fluffy, that's okay. However, unless you have a Ward Save as well, then the MoT is wasted. A WS7 Character, such as the Exalted Champion instead will benefit against WS4 opponents in a challenge, meaning that they have to roll 5's to hit.
The Dawnstone is okay - but as said, it doesn't stack with the MoT. If you want MoT benefit, then the Talisman of Endurance is where it's at. However, you'd give up ASF for that - giving yourself a Sword of Might will give him 4 S6 Attacks. Combine that with a 3+/4++ Save, or a 5+ to hit with a 3+ Save.
Exhalted Champion
Shield
Mark of Tzeentch
Chaos Runesword 175
Disagree with this. The Runesword is built for Lords, IMHO. It stacks with their abilities, but is too expensive for Heroes. They could do with some other abilities. Namely, you're missing the BSB for the army - You have Ld8 in total. Even a couple of extra additional CR points will see you break. A BSB will turn I think what is a 72% to 92% (although usually it's going to lower Ld).
19 Chaos Warriors
Full Command
Shields
Mark of Tzeentch 354
Good.
19 Chaos Warriors
Full Command
Shields
Mark of Tzeentch 354
Doubling up isn't generally a bright idea. Your army is lacking hitting power. Instead, try MoN, Rage Banner, Halberds and Shield, with Full Command. Expensive, yes. But so worth it. I've yet to really run an army for WoC without this unit at some point. Infantry are the new killing power for WoC, whereas it used to be the Knights in 7th.
If you take the above suggestion, then this unit is the sacrificial one. Apart from Ogres, they are possibly the most useless unit in the army. However, they were fast, and cheap, hence expendable. With TLoS now, they can't block Knights.
Special
10 Chaos Knights
Full Command
Mark of Tzeentch 470
WAAAAYYYYYY too many. You've got over 200 points locked up in +1 Combat Resolution and 5 Attacks. Does fack all. Split the unit into two at least. That removes the whole "Shoot me" banner they're waving.
Personally, I'd spend a few hundred points on giving just 5 or 6 of these Knights a Blasted Standard.
I'd put the rest into a unit of Trolls or Dragon Ogres. They're hard as fuck, as long as you keep the General and BSB nearby.