Looks very nice on you! Don't apologize about the shirt. I think blue works well with that tartan. It helps to pull out the light blue lines. I even like the sweater vest, though I'd advise that the sporran is too formal for the rest of the look. Though I understand you are just wearing it to show off your new toys!

I think a simple leather sporran would work very well with a casual, sweater vest sort of look. In fact, I wear my sweater vests with kilts frequently!
M