I forgot to mention that these drapes will be unpleated panels on clip rings.

Different books/instructors will have different methods of construction, so it's more a matter of preference, than right or wrong. I prefer a double 4" header (or possibly a double 3"). I'd add buckram in the fold if you don't want any droop between the clips.

I would suggest a double 4" header with bucram. You can get help from the pros at www.chfschool.com