How would you round out this collection?

You can magnetise the chariot. Only the guns and their mountings are different, so you can just swap out the whole mounting. Just be a bit careful where you position the MoW's right hand, as it's supposed to be resting on the gun.

I really like the Assault Chariot. It's fast and really dangerous into swarms, so it covers two big weaknesses of AC single handedly.

That said, both colossals are very good choices. You can't really go too far wrong with either option, although the chariots are more hotly disputed and limited to one theme.

As for mercs, I've become very fond of Ragman in AC; they love a bit more damage, he loves super-durable troops to sac pawn on to and reach troops to Death Field. Good synergy there.

Another Strike Tanker to give you full force there is also a reasonable option.

And maybe Sorscha3 as a caster.

On the topic of colossals, what main purpose do you see for them? Supporting the rest of the army with their big guns or getting into the fray as quickly as possible?

What do you mean by the chariots being more hotly disputed? As to which is better? As to their vuability in general? I’ll admit that one regular opponent often fields Siege Animantaraxes and I look at our chariots in comparison... and yes I know the derp turtle is a few more points, but good grief, those things are stupidly OP, imo.

A second strike tanker is noted.

Any other warjacks that you think are crucial? Having shifted to vlad from butcher, I’m trying to get used to playing non-character warjacks. I think my next several games will be with a destroyer and kodiak, though I fear I’m getting utility but losing power. But maybe that’s what feat turn is for :-)

Certainly the former. A colossal can't lead the charge, not least because they're too slow and unwieldy. They do insane amounts of damage, but if you overcommit with them they will go down. I use them as a big old chunk of control. Plonk one just into a zone, and it can still cheerfully affect the battle with their excellent guns, and there's nothing your opponent can do to shift it short of actually removing it since they ignore basically everything. If you've got a caster who isn't great at providing focus to multiple jacks, having one massive jack plays to their strengths.

I'm a big fan of a Destroyer in lists these days; much like the colossals, you can toe a zone and still affect the battle. And Arcing Fire means that sometimes you can snipe out something important. Kodiak is great, Juggernaut is great... honestly, every jack in the 10-14 point range in Khador is pretty damn spiffy (Not you, Drago). I even like the Grolar and the Berserker outside of that range. Khador has a really broad jack stable these days.

Chariots! By disputed, see borderprince's reply. He doesn't rate them, and I think they're extremely good. I wouldn't worry too much about comparing them to other factions' stuff; sure the Animantarax is great, but we can't take it anyway so it doesn't actually matter. Hell, the Gun Carriage is better in faction, but again, can't take it in AC, so who cares?

Why I like them is because of the pressure they allow you to put on your opponent, and how their insane speed lets you dictate the terms of engagement. You can threaten basically the whole board T2 thanks to the Advanced Move, and I find that they often put my opponent in a bad spot because of it. They can also make some very disruptive plays, knocking down several models and splattering support solos/units. Even if you have to sacrifice them in the process, sometimes completely screwing your opponents' timing is worth it.

Soar - sha.

That is how it is pronounced.

Triple marauders is my favorite thing right now. Great into big bases obviously. But even so, slams are fantastic for the medium infantry spam. POW 20 still hurts. Paired with vlad2, a 3-8" slam is money. You also have 3 khador heavies the opponent has to worry about ontop of your massive amount of AC bodies.