I'll be honest and say I'm not sure what you are actually asking, if you are looking to pleat to the stripe then the calculation you really need is how many stripes that will make up the back of the kilt, and add the equivalent of two front aprons width to make up the final ammount of length. So, for example on a 36" hips measurement, you are looking at about 18" for the back, so you need at least 18 stripes if pleats are about 1" at that point,that is fine for an 8yd kilt( although I would actually add a few more to bring the with down to about 3/4"), but the pleat width could be between 2"-3" on a 4 yd kilt, so perhaps somewhere between 9 and 6 stripes on that style.
I wouldn't get to worried about the actual sett size if it's anywhere 6"-9" that's relatively common and most kiltmakers would be happy to work with that.