I would advise you to get your ticket early for the Tattoo - they sell out very quickly. Travel companies buy them up in bulk.
I wouldn't worry about wearing your kilt, barmen in Edinburgh are used to seeing just about everything, particularly during the Festival in August. And don't worry about the locals either, they will probably be wishing they had worn theirs. Sadly, like any large city, there are bound to be a few "low-lifes" about who might make a comment but that is more likely if they hear an English accent rather than an American one.