Those Pendleton blankets that are white with the red, green, and yellow stripes usually go across, but I can see where on a king size it might look better longwise. I would just do what you like. You are the one who has to look at it.

I would run the stripes up and down from head to foot. Stripes running vertical will be much more forgiving if the bed is not made perfectly. If you have the stripes running horizontally, you will drive yourself nuts trying to keep them looking straight. (I have stripes on my reversible comforter, and I've learned to always run the stripes vertical for this very reason)

Of course, the thicker the stripes the fewer there are and, consequently, the easier to keep them straight. Then it's probably just a matter of personal preference.

I think you are talking about making the "tubes" into which to stuff the plumes or feathers? If I have understood correctly it is always horizontal and each tube measures about 5-6" wide - just keeping adding till you reach required bed width (and a little over)