I think the whole outfit sounds MORE than fine. And I think you were wise in hiring a quality kilt and jacket since you couldn't have one for purchase in time. I think either tartan is completely fine. They're both fine tartans. And a black Argyll compliments ANY tartan. The fact that you're looking for formal attire buttons that question right up. If it were me, the only change I would make would be the hose. Creme hose are fine, but I, like many others, have grown to really love a colored hose. I think navy hose would look smashing with everything else you've put together. Just my two bits. Enjoy the prom!