Unless you're pretty substantial in your girth, five yards should suffice. Much more and the thing gets too bulky.

I would think that someone would be able to make a double width run if you're paying for it. But then, I can't imagine that you couldn't sew two pieces together. Assuming that you aren't too tall, a little less than 56" should work fine. Just know that the seam will be above your waist and might show a bit right in front. I'm about 6' - 3", and I only wear a 24 1/2" kilt length, so a seam at about 28" is bound to show a little. But creative rolling of the material over the top of the belt will minimize if not outright hide the seam.