Yes, I would go with white shirt, Argyll jacket, black tie, tartan flashes. No weapons at a school event. No belt nor fly plaid needed.

That should leave you needing just a black sporran and a vest (waistcoat) to match your jacket. I'm not familiar with the sporran TB is referring to but consider your vendor carefully, I have heard good things about Celtic Croft's service.

Moosedog