Personally, I would do the following:

  • change hose to a cream, oatmeal, or a blue or green that complements your tartan
  • change ties to a blue or green that complements the tartan
  • if you've already gone with blue or green hose, match the tie to the hose
  • untuck the tie and use a tiepin or tack as necessary

As for the shirt sleeves - I've seen enough well-dressed men in short-sleeves and ties that your shirt looks fine to me.