It is a s you say hard to find accurate information as heraldry was in it's infancy still at this time and we only have one rather poor illustration that I am aware of for him. However his arms and armour etc would have been the same as any other knight of the period, his face would be a matter for yourself I don't think anybody can state with any authority if your face is right or wrong. I would be tempted to paint his shield as per the flag with the arms of England at the time, certainly that was the custom for the standard bearer in later medieval times. The flag at the time would have initially used a single lion rampant, or else two lions,it didn't change to 3 till around 1198. Hope this helps
Steve