Don't want to hijack the thread or throw a wet blanket on your impending celebration, but if your kilt is in customs at FeDex you should probably be aware that you will likely receive either a phone call or email from them about import tariffs (depending on the material and value of the kilt as listed on the shipping manifest) as FeDex is a stickler about collecting customs fees, and then tacking on their own additional handling charge to boot. It may not happen, and if so I will be happy for you, but it is better to know about it in advance rather than be surprised and shocked when they contact you.

On your waistcoat dilemma I would listen to our style gurus McMurdo, Panache, and Jock Scott for the best advice. Realize though that it is only advice, not a dictum. Wear what you think looks good.