How much is too much is a personal choice; look at the uniform of the Gordon's or Seaforth's and count all the deer heads, or harps on a piper from the Royal Irish Rangers; a common theme is pretty traditional. I would point out that most people will only see the top 2" or so of a skian dubh, and if they see your kilt pin up close...well, I hope that they're a very good friend. A clan badge on your belt buckle and your bonnet will get the most use at Highland games and whatnot.