The difference between good spats and bad is tightness. Button the two parts together and fold them in half along the toe to determine where the center back seam should fall. Pin them loosely together and fit them over shoes and stockings. Backstitch for strength. If they are hard to put on, they are made properly.
pockets are British Army style, but slightly higher. Keep in mind there is scant evidence for belted waistcoats, so interpretation will be conservative and familiar. The front is made of white cloth and the back of serge. No vents or tails, the whole thing is tight.
The bottom is cut square, but slightly lower at the front to match the tilted waistband on breeches and overalls. The vest covers all but the lowest button on the pants. A period button formula has a space of two button widths between each actual button, so between ten and twelve buttons depending on height.