As is stated above, I'd be far more concerned with the fit of the existing items before adding any other items to the closet. The kilt is not being worn properly, it is far too low. The waistcoat appears to be too long, but I can't really tell. It might be a waistcoat made to wear with pants, and that would hang too low. The shirt doesn't seem to fit well.

Bottom line, take him to a kilt shop. Have him properly fitted up and down. Then start buying the rest of the outfit.