Lithium, welcome to the One Ring!
If you are using the Fallen Realms Sourcebook (providing you are using sourcebooks at all) then I would personally go with a semi-elite cavalry of evil men. Morgul knights for the hard-hitters, Easterling Kataphracts (sp?) for the 'generic troops,' and Haradrim Raiders or Khandish Variags for bow-equipped nuisances. If you feel like using bow-armed troops.
As for the hero, personally, I would get a few dragon knights or equivalent caliber heroes in there for the actual fighting, while using Wraiths for the "commander" equivalents of the troops, to call heroic moves and such. The Knight of Umbar, Khamul, and the Witch King are all capable of taking care of themselves in combat, but the Dwimmerlaik might benefit you by minimizing enemy countercharge. Particularly if you team him up with Gothmog on warg (which, if you are using warg riders, I personally think you should use) because it could be very painful for the enemy to call a heroic move at that rate. Also, War Priests could be good if you decide to use Easterlings (providing they can have horses- sadly, I don't remember off the top of my head). The Mouth of Sauron is a nifty addition of a little extra hitting power, with a few transfixes to boot.
My cavalry experience has always been mostly with Dol Amroth and Rohan, where I have found that a mix of heavy cavalry and light cavalry can work well- but have a plan in case they go Thermopylae on you. Playing evil by way of Isengard, I know the usefulness of forming the pincushion of death.