I played against a similar thing with my chaos, while preparing for a singles event.
Ideally, you'll want to do damage in the shooting phase, so he's weakened when he gets to you. I had all my squads equipped with lighting claws, so they did almost nothing (lol).
A khorne lord, with the Axe of Khorne would be handy, due to striking at Initiative at Ap2. Powerfists I would almost recomend shying away from upgrading melee weapons on squad champions, for the most part, as they will not do a whole lot (but if you have points to spare, a power axe or two woundn't hurt).
For shooting (and I recommend getting units which can shoot), you either need to swamp him with saves, or have a lot of AP2. For the former, heavy bolter havocs can dish out a lot of saves, same with Chosen/havocs with flamers and Predators with autocannon/heavy bolters
For AP2 shooting, Chosen or havocs with plasmaguns are nice, as well as obliterators and Vindicators.
For dealing with the landraider, it'll be hard to kill before it can disgorge it's ocupants. Might be best to invest into some cheap units to act as shields for more expensive units, but small enough, so that they will be killed on the charge. Cultists, or 5 man marine squads for example.
I run mosty just a high number of 5 man squads in my marine army, which means if any unit is charged by something scary, odds are they will be wiped out, allowing me another turn of shooting. Nothing worse then having an enemy unit locked in combat in your turn.
Daemon Princes can also work, they can dish out a lot of damage at AP2.
It all depends on what you have and are willing to work with. At 1250pt, I recomend taking as many small squads as possible. Try to spread him out and win on objectives. If you outnumber his elite units, he will have trouble dealing with all of your squads. I would be hesitant of spending lots of points on lords and such with only T4, as they will be instant killed by power fists and the like.
I donno, I might take something like
Sorcerer ML3 (roll on biomancy or Telepathy for
low AP attacks, or ignoring saves)
Lord MoK Axe of Blind Fury (
high initiative, low AP attacks)
x6
Chaos Marines
x5, x1 plasma or meltagun two squads with Rhinos
two units of two obliterators
Unit of three terminators, all with power axes and combi-meltas
Terminators deep strike, obliterators can do as well, or deploy. Squads keep together, but far enough away to not be double-charged. Lots of Ap2/1 shots to either kill marines or tanks. Lots of objective secured, which he'll be lacking. Rhinos are good for moblility, or keeping squads safe from shooting. Lord and sorcerer support infantry squads and have the ability to damage mostly anything.
Because there are so many units, it'll be hard to pin the army down and you can be quite casual in sacrificing the squads if need be. They will die easily, but there are so many you can swamp objectives. If the mission is kill points, that'll be more of an issue. I'd probably resertve things.
I think with chaos, as things are often not fearless, large squads are a liability. Two five man units are more flexable and can still work together.
Really though, there are a lot of options. You could take three maulterfiends and a bunch of hellbrutes and wash him with your own armour. Really, try seeing what works and move from there. Keep tweaking your list between games and you'll eventually find something that works
Excessive stats purged to please Khorne - Iris.