When worn with a homemade breastplate and cape, you have an instant knight. Another thing to have on hand is 2-sided fusible pellon or webbing. A couple of brand names are 'Wonder-Under' and 'Heat 'N Bond'. Utilize the books you read for costume ideas. In this case, there are books specifically on the Uniforms of the Civil War.
Imagination makes up for all the shortcomings.
My daughter had duel roles of Union soldier and Clara Barton. When she wasn't in a skirt, blouse and apron, she was donning the blue blazer and cap. I found a gray and a blue wool suit coat at a Goodwill store. I next purchased remnant yellow fabric, enough to treat the collars, designs, cuffs and to make two sashes. I found the cheapest brass-looking buttons I could find.