Possum,
Firstly, welcome to the forum. There are a great deal of current, prior, and retired military on this forum from several different countries. You are among friends.

Regarding your question on rules about the kilt, etc. There are absolutely NO provisions allowing the wear of "the kilt" to a US Army official function (I guess I should end that sentence with the words "that I am aware of"...but I believe it to be absolutely truthful without that caveat). AR670-1 does not authorize the wearing of non-regulation garments such as the kilt with the uniform (though I think the mess dress jacket would look superb with a kilt). There are several other threads here where you will find spirited debate about bending the rules, etc. Some here don't see it as a big deal. Others feel that part of the prestige and professionalism of the military is strict adherance to uniform standards, etc. I guess I fall somewhere in the middle. I don't think I would wear a kilt to an official function where I'm expected to be uniformed. I would definitely wear a formal kilt outfit with mini-medals to a military event or other social event if I were not required to wear my uniform (ie...a non-unit event). I hope that answers your question. Feel free to hit me up via PM or pose further questions on here and I'll do my best to answer them with facts and my opinion as a field grade officer (for what it's worth!)