I think the overall look is quite nice, personally I like the look of a solid tie with tartan, so I think the tie is a good choice as it does match the blue in the kilt very well. As you are a guest I think perhaps you should change out the sporran, depending on the time of day the semi formal may look more appropriate. Ghillie Brogues are a matter of personal taste, for a wedding though why not wear them. One last thing, before you go to the wedding be sure to wash your face.