FWIW I've seen chaps with regular kilts, nice boots, a medievalish vest of some sort and that lace up ren fair shirt and they fit in quite well. Sure, not authentic, but neither is anyone else aside perhaps from a dedicated reinactment group and possibly some of the hired talent.

I'm doing the great kilt ren fair thing as well. I got the Celtic Croft braveheart tartan great kilt, made my own rob roy sporran, and finished it off with the CC ring belt. Made some crude ghillie brouges, picked up a simple balmore in blue, and got the longest tailed shirt I could find (it does have laces in the front, but the wife prefers that look so I defer to the lady This about completes the outfit, all I have left to do is shape the balmore a bit and get a pin of some sort to hold the ends of the kilt together (decided not to do the perannular broach, though I think it is a good look and not horrendously inaccurate, especially once I hang my drinking mug and whatever dagger comes to hand off my belt . If I get sufficiently motivated I'll knock out a targe of some sort.