The Breamer Ghillie jacket looks like a 3 button version of the classic argyle jacket.

Since weddings are not usually black tie affairs (unless celebrated in the evening post 6 PM I believe) wearing a 3 button argyle is perfectly appropriate and some would recommend tweed vs the more formal barathea. I believe barathea is a particular weave. http://en.wikipedia.org/wiki/Barathea

If warmth is a consideration you could get a linen jacket and waistcoat made.

Either way I would heartily recommend the 3 button argyle look. The square buttons used in highland jackets are fasted through a "buttonhole" in the fabric with the small metal clips you mentioned so having it made for removable and swappable buttons is definitely possible and a very good idea.