It sounds like the general concesus is to go with a tweed jacket with/without a waist coat and maybe without a tie and the most casual sporran I own which would be either the Rob Roy or the plain black with Sam Browne closure. Most of the sweaters that I own are crew neck so a tie might not be fesable. If I went with the tweed jacket and no vest, I have a couple of black kilt belts with not too shiny waist plates.