Thanks for you clear answer.

I allready decided to pleat to 1 stripe and I ordered enough tartan for the job.
I never thought about the box-pleated kilt. And I like the idea but my customer absolutely won't go for that.
He's a piper (although the kilt is not for band-use), and I'm sure (read: I know) he wants his kilt in the traditional knife-pleat-version.