Personally, I think that is the perfect outfit for a "casual" wedding. If it were me in the same circumstances, I would probably wear something very similar. Perhaps no vest, but then again, I like the look of a vest with my kilt as well. Also, I might wear my plain black leather sporran--but then again, I might wear my fur too (which is similar to yours). But I would certainly dress down the sporran before loosing the vest and tie. If that makes sense...