If it were me, buying these things for a wedding but planning to wear them in Scotland at a "black tie Highland Chieftain's Ball", I would most definitely try to stick with the traditional Highland customs so as not to look 'touristy' at the latter event.

As to hose, claret/maroon would be perfect. White or ecru hose may be worn, but can have a very generic look to them if they're not very thick.

For flashes, definitely stay away from tartan flashes. Plain red flashes (with a very minimal amount showing) would be better. Or even better than that, woolen garter ties. I always favour red, regardless of the tartan. But in your case, red garter ties would look strange with claret hose, so perhaps yellow would be perfect since the MacPherson dress tartan has a yellow line.

On shoes, I would go with plain black polished Oxfords or a cap-toe shoe. Wingtips (brogues) really aren't the best shoe for this level of dress, even though it is occasionally done.