sounds great! that would be the Nguni impi special ability I think :-) though I think that reducing the hit chance to absolute 0 is kinda pushing it. Maybe 70% reduction? (30% chance of hit)
Yeah this figure can be changed through play testing

Hmmm would it be possible to use the horses as the basis? Fatten them up, shorten their legs and add horses
Well I was going to use the basis for the horse model anyway but it may mean changing the skeleton and I am not so sure on how to do that

and who got slaughtered before the battle was over I think
Yup, your right there. It was the first battle where the winners came and slaughtered all the surviving enemy, including women. Thats why it's such an important battle in the history of tribal warfare.