Just my personal take on this - if someone really wanted a stars and stripes kilt design I would have a blue fabric with small amounts of red and white in the weft (vertical in the finished kilt) maybe two threads of colour two of blue then two of colour at intervals of one inch, colour alternating red and white. With such a small 'sett' the kilt could then be made with alternating pleats having a red or white line either centre or I would put it close to the fold so the alternate stripe flashed easily.

I might try having the same colour stripes one every 6 inches in the warp just to make it more tartanish, but I'd need to see it first.

At the edge of the apron I would attach a vertical band with two lines of small descrete stars on blue, and a fringe of mostly blue but with red and white included.

I would have the star band made with the proper number of stars(which I believe is 50?) in two counterchanged rows and then a blank strip so that the stars could be fitted onto - say 20 inches, and the blank area would then extend the band up to maybe 26 or 28 inches, plus a hem allowance.

This is of course making the kilt more flag like, but it would not be right to have parts of stars so each kilt must have its own full set of whole stars, and that being the case only the right number of stars would be correct.