Be comfortable, flairball. Forget the waistcoat. Don't worry about the braces; don't button the jacket in some effort to hide them, in other words. Your sporran should lie a hands-breadth below the buckle of your belt, and the belt should be at your natural waist. I'm not sure what you mean about wrinkles in the apron and a need to distribute them, but I think you worry needlessly. Relax and enjoy the occasion.