Tolkien has very little information about the physical appearance of the Balchoth, so there is nobody to tell you your own vision is wrong. Picking available figures from any largely infantry culture involved in mass migration would work. Examples of appropriate cultures include Early German, Gauls, Ancient British, Pictish, Irish, Minoans or Mycenaeans, or even Classical Indian. Wagons for the Horde can be constructed or purchased separately.
My personal preference is Early German, Gepid, Visigoths and the like, possibly Dacians. I like the hairstyles.
Ancient British chariots work well for battle taxis.