Looks great! I would probably give his helmet some white feathers to show his rank a little more. Either that or change his helmet for a round hat with white feathers:
Oh and a note about the sash. That is the sash of the order of the garter, I believe it is a little more light blue in colour and is worn from the left shoulder to the right hip rather than the other way around. Here is a portrait of the King wearing it. It was his favourite order:
I say that but Sir Edward Walker (he was pretty much the Kings's secretary, he is the guy sitting down writing) is wearing what looks like the sash of the order the other way around unless that is another heraldic order.
EDIT: If you are thinking about doing a Parliamentarian General then here is a picture of the Earl of Essex, it is not in colour sadly:
His sash would be orange/tawny since that was his personal colour, he seems to be wearing a breastplate and I expect the rest would be in buff (except perhaps the trousers, red maybe?)