Although there were black legions in the Roman Army, you didn't have single black legionnaires at this time in history. The legionnaires were too young, and they kept referring to each other as centurions which is a rank equivalent to a SNCO today, not an 18 year old soldier. Plus the horse hair crest on the helmet of a centurion was cross the helmet not front to back.
The plate armor worn by the legionaries does not match actual reconstructions. Also, the legionaries would have worn either plate armor, mail armor or scales, but certainly not a combination of those, which would only be impractical and overly expensive.
When setting out to look for the 9th Legion Bill insists that they would have followed the river, however there is no river running south from Scotland to England. In particular there is no river running from Scotland to York which, as the nearest (still standing) Roman outpost and their point of origin, would have been the soldiers destination.