I find it easier to figure out what is "appropriate" in more "dressier" situations than casual ones re: wearing the kilt. Just make everything above the waist pretty much like what others will be wearing and the rest coordinated/appropriate to the tartan of the kilt. On the other hand, as father of the bride, I would think you could wear pretty much anything you want just as long as you not "outshine" the groom (or bride, which you couldn't do anyway, no matter what ).