If it is white tie then a white vest is worn with a white silk tie. Your sporran is really a day wear sporran not meant for formal functions. But I'll assume its the only sporran you have so it will have to do.
The whole belt issue is confusing to new wearers. Highland wear outfitters are in the business to sell. And that includes belts. But its kind of hard to sell belts if none of the models are wearing them. A fitted kilt should be able to stay on without a belt. So that make the belt a bit of decoration. A vest/waistcoat would cover the part of the kilt that the belt is worn. So then it would not be seen, other than an unsightly bulge.

I am seeing a bit of shirt sticking out between the jacket and kilt. This usually means that the kilt is worn too low or the jacket is too short. Is there any way you can pull your kilt up a couple of inches? It looks like you hem is hitting mid knee. Its an odd camera angle, so I can't tell. Kilts are worn higher than normal trousers. An inch or two above the navel is about right. Some could be worn higher. Your vest will cover the top, so no one will see how high it is worn.

Not bad for a first try. There is always room for improvement and that's what this forum is for. I would say that most of us did not get it all right the first time we tried it on our own. And you are not in an area know for its kilt wearing so I doubt you've had any instruction other than the interweb.

Best of luck. And we do want to see pictures from the ball.