If you're going for "gunline chaos" I recommend Noise Marines rather than Thousand Sons. Not only do they do a lot more shooting at a much further range, but they're not Slow and Purposeful and pretty good in close combat as well, so if you end up in a situation where the gunline tactic fails (drop pods) you're not screwed.
Also, I'm personally not a big fan of giving big guns to something with a 1/6 chance of shooting that big gun at my own guys. Personally if I want a walker for CSM, I really like Defilers.
Missile Launchers for the Havocs might also help make them a bit more multi-purpose, but you also have a decent amount of anti-horde anyway so that one's pretty debatable. Or you could go for Obliterators so you don't need to make that decision. For how much 4 Lascannons cost they're not that much more expensive, give you multiple options and are harder to kill.
Also if you're going for a shooty prince, don't underestimate the true power of Mark of Tzeentch. The fact that you can take Bolt and the 4+ save are cool, but there's also the fact that you can take a second psychic power and use both in the same turn. If you read what the codex says, it also says that you can only use one shooting power because models are limited to a single ranged attack per turn, but monstrous creatures are limited to two rather than one, so you could probably argue that you could fire both Doombolt and Bolt of Change, for example, as long as they're at the same target. I'm also a big fan of Gift of Chaos, particularly against Eldar or Imperial Guard, where they have lots of very important low-toughness models.
Also, I'm personally not a big fan of giving big guns to something with a 1/6 chance of shooting that big gun at my own guys. Personally if I want a walker for CSM, I really like Defilers.
Missile Launchers for the Havocs might also help make them a bit more multi-purpose, but you also have a decent amount of anti-horde anyway so that one's pretty debatable. Or you could go for Obliterators so you don't need to make that decision. For how much 4 Lascannons cost they're not that much more expensive, give you multiple options and are harder to kill.
Also if you're going for a shooty prince, don't underestimate the true power of Mark of Tzeentch. The fact that you can take Bolt and the 4+ save are cool, but there's also the fact that you can take a second psychic power and use both in the same turn. If you read what the codex says, it also says that you can only use one shooting power because models are limited to a single ranged attack per turn, but monstrous creatures are limited to two rather than one, so you could probably argue that you could fire both Doombolt and Bolt of Change, for example, as long as they're at the same target. I'm also a big fan of Gift of Chaos, particularly against Eldar or Imperial Guard, where they have lots of very important low-toughness models.
