Well alright we have some information to work on. So through my traditional Highland Scots eyes I would advise no PC as the wedding is clearly during the day. As you are piping I think a black barathea, silver buttoned argyll and four in hand tie(not a bow or one of those dreadful ruche tings). In truth it would be more traditional for a piper to wear a tweed argyll for this sort of event that appears not to be going too far, down the formal route, but I am adjusting my advice a tad to take into account a possible need to "over dress" a tad, due to your local conditions!

Avoid like the plaque, those dreadful ghillie brogues and those even more dreadful "semi dress" sporran things. Good well shone up black shoes and a black day sporran will do nicely.

Just my thoughts and shoot me down in flames if you wish. Have fun!