I've always thought that polos would look fine with the kilt, just don't really own any as they don't fit my personal style. Only have one which was free from Kryptonite bicycle locks and is about 20 years old at this point. Also fully agree with the button up short-sleeve shirt as a great way to go, though I would also find the waistcoat and short-sleeve to be an odd look. We were hitting the high 80s last sunday and as it was youth Sunday meaning I was the officiant mostly in appearance I could dress down which meant short-sleeve and certainly no vest.