In Khergit territory, though, mountains are never far, so if you have decent pathfinding, you should be able to make it to better terrain before the horde catches up to you.
Yes, if the hills are large enough to allow the Khergits to ride around on the tops, then you should be just below the crests of the hill, so your men are sheltered from archers on the top. If the crest of the hill is small enough that your men take up about half the space, then I'd stay at the top. There won't be room for the Khergits to maneuver.
Also, another tip, bring a good bow and two quivers of arrows. You'll be able to stand amongst your men and take advantage of their shields, so you shouldn't need one of your own unless you plan on being heroic. If you're a good shot, you can turn the tide of the battle with several well-placed arrows. Not to mention that hurling pointed sticks at high speed into charging Khergits is extremely satisfying.
The only time you'll be engaging in melee combat is when you're cutting down disabled horsemen, so I prefer a two-handed weapon. Preferably a Balanced Great Axe.
Also, if you're okay with it, take along a few Hired Blades for a bit of party speed. You'd tell them to dismount in battle, as you don't want them to try to chase the Khergits. They can hold their own on foot, and they usually have shields. Swadian Knights would probably work, too.