MoR gives some excellent advice. The one thing I would add is that since ghillies are a one-purpose shoe and regular oxfords, cap toe shoes, wing tips, or just about any other good black tie shoe will serve non-kilted purposes as well, don't pay the extra money unless you really like them.

I alternate between a black cap toe shoe with a kiltie attached for moderately dressy wear, a cap toe blucher oxford in cordovan for day wear, and a plain toe, spit-shined black oxford for black tie. All of them can be worn with any type clothing.