From the looks of it, you won't be coming up against land raiders or nightbringers very often. Therefore, you need swarms.
Think about this: I could get 1 Chaos Aspiring Champion with maybe 2 upgrades for 42 points, OR
I could get an entire command platoon with Imperial Guard for the same price.
I strongly suggest mass guardians. 20 Guardians and 2 Scatterlaser Platforms is relatively inexpensive, strong guns, able to take down all tanks that you'll face and you can add warlocks. Put in very small squads of rangers to disrupt your enemy, and maybe a storm squad for close combat.