Just to make your decision more confusing, I would wear the cream hose and red flashes. (I'm not familiar with your tartan, I presume it has some red in it for the flashes to pick up?) My best pair of hose are cream and were knitted for me as a wedding gift by my sister. I wear them all the time and I think they look swell. As a disclaimer, my tastes aren't as traditional as many members here.

For the sporran, I agree with Brooster. Wear the plain leather.

No matter what you wear, there will probably be no one there who knows the traditions of highland fashion. So wear what you think looks good and walk proudly.

David