Tweed epaulettes

[McMurdo]

How important are the horn buttons? My kilt jacket currently has the leather covered buttons found on many tweed sports coats. Is that a major faux pas for THCD?

Either works well, unfortunately these days the imitation kind are all too common. My oldest vintage kilt jacket has leather buttons. I also opted for leather buttons on my bespoke tartan jacket and waistcoat. If you can get real horn buttons then by all means do it, however they are harder and harder to find and the imitation kind are so prevalent that nobody will think twice if that is what you have.