It rather depends on the weight of the fabric you intend to use, and the style of the kilt - but I would recomend a closer spacing if you want even a semi traditional look.

I make my kilts and have settled on the Kinguisse style, either the original or the reverse. These are pleated with the two sides mirror imaged. The Kinguisse style has pleats which open to the front, with a box pleat at the back. The reverse has the pleats opening to the back, with a reversed box pleat centre back. This reversed form is better for moving through vegetation as it does not get snagged so easily.

The kilt I am wearing at the moment is 50/50 cotton/polyester, and lightweight due to the heat here. It is kinguisse style, with 7 inch pleats. That is the visible folds are 7 inches apart on the small pleats. The 'show' is just over 1 inch, and the 'cover' is just under 3 inches. The under apron folds are 6 inches deep. The visible part of the box pleat is 6 inches.

I made a number of kilts with similar sized pleats before I really began to loose weight, and have remade some with 8 inch and 9 inch pleats, and I think they do look better with more fabric in the pleat.

I did have the luxury of having considerable amounts of cloth already, and so could find 7 yards and more of fabric quite easily, though the weight was good quality dressmaking. I have bought heavier cloth since but have stuck to the same 'show' and depth of pleat.

With a non patterned fabric I do tend to use the whole amount I have available, so I measure, divide up the sections approximately into apron, pleats and under apron, and then divide the pleated length as appropriate. Oddly it tends to resolve into whole numbers of inches.

If you are using a thick or closely woven material it might limit the size of the pleats as you will not be able to sew through multiple layers, so there you will have to try out your sewing machine or the strength of your fingers on small test pieces to see just how many layers you can cope with and design with that as one of your parameters.

Of course if you are really thinking of a modern design you could form the pleats and then glue them in place, or drill and rivet them, or use a material which can be welded....

Whatever the method of construction, a cloth with a slightly open weave will swing better than one which is more rigid - for instance the only Utilikilt I have seen had no flexibility at all. It was made from black denim like material and it oscillated like a bell rather than undulated like a 'true' kilt - it was also flared, not straight down from the hipline.