Well it seems you like the cavalry theme. If you're getting knights I would recommend Marauder Horsemen to support them. Or if you would like to be fluffy maybe some flesh hounds.
I personally don't trust knights unless they are chosen with the mark of khorne and Banner of Rage. Otherwise, they're not getting enough attacks. Facing an average infantry unit knights already need 4 kills(3 ranks, 1 outnumber) to equal the combat resolution of the unit they are facing. My Chosen Knights of khorne have won combats where they were engaged in the front, flank, and rear and still came out victorious.
Make sure you screen them though. They tend to be very nice target for the enemy.
Lastly, since most of your points will be used up in the knights, I would probably recommend going with marauders to bulk out the rest of the army.