How wide do you make...

[HeathBar]

Matt Newsome at the Tartan Museum actually offers Great kilts with the pleats stitched in either box or knife. Although if you are going for period reenactment, I'd go with knife. And leave the apron edges as they are.

Matt wore a great kilt he had done to a Burns Dinner. I can't remember if he was in a PC or Argyle jacket though.

[M. A. C. Newsome]

If you are looking for mid-eighteenth century, I assume the look you are going for is an untailored great kilt (which would be accurate for that period), and you are simply sewing the pleats in for convienience. That being the case, I'd just side pleat them (knife pleat) and be sure to leave them unpressed.

I do this for people on occasion, and I can do it different ways depending on what look they are going for and how accurate they want to be. You could center each pleat on the same stripe, which would make the kilt look like you spent some real time arranging the pleats to get dressed. If you want something that looks a bit more like the feilidh-mhor would have normally been worn, don't pay any attention to the repeat of the pattern. Just decide going in how wide you want your pleats to be and do the math, irrespective of the sett size. If you really want it to look like you could have just arranged the pleats by hand, you can even make your pleats various sizes and depths.

I sew the pleats down about 2" at the waist only. Then I add a couple of belt loops, which I find makes wearing the feilidh-mhor a bit easier, as it keeps the belt right in line over the stitching, making sure that the material doesn't slip and let your "cheater" stitches show!

As for the edges, I use a self-fringe. Just pull the threads out of the cut or ripped edges of the cloth until there are no more loose threads. After about a quarter of an inch or so it should be harder to pull a thread without picking at it to get one loose (assuming you are using kilt-quality tartan cloth). At that point I just leave it naturally fringed like that.

The great kilt I wore to our Burns Supper was a bit different from this. I wasn't wearing it for reenactment purposes, but for modern formal wear. I box pleated it and pressed the pleats all the way down, like a modern kilt.
I wore it with an Argyle jacket: