Draperies and Top Treatments - Where do I begin?

I recently purchased some draperies from Restoration Hardware (Silk taffeta, Inverted pleat, 120" L x 48" W, quantity:2, Cat # 1320.1007) to match our bedding and paint scheme in our master bedroom. The wall slated for the drapes is 15'-4" wide, 9' high at the left and right edges, and 12' high in the center (vaulted ceiling).
The window is a box type with seat, height 9'-5" and 6' wide, centered laterally on the wall. My plan is to hang the drapes outside the window from a traverse rod anchored underneath or to a small crown-moulding-rimmed shelf projecting from the wall at some arbitrary height above the box window. (Would this be a box cornice?) I may have to have the drapes' length altered, as I don't think the full 120" height will look right.
The drapes will be opened and closed daily, and I may automate the traverse rod.
My questions are- How long should the traverse rod be? Are two drapes 48" wide going to be wide enough to cover the window when closed? How much should be allowed for the stack on each side?
p.s. I've used all the drapery vernacular I know. please keep any responses simple enough for a mechanic to understand! Thanks.

Hi and welcome to the forum! Generally, you'd multiply the window width by 1.3 to figure your stackback in order to clear the glass and that would give you your rod length. Since your draperies are readymade, you'll need to to figure your rod length by the width of your draperies. Inverted pleats don't stackback as well as pinch pleats unless they have small pleats, but I can't tell without actually looking at them.
Normally traversing draperies include returns and overlaps and some ease (so they don't pull), but again, without looking at them, I don't know what the 48" includes.
If you need them to close without any light coming in, you really need to order them first and fit the rod to the draperies instead of the other way around.
I'd say the 48" can be hung to close with a slightly smaller length rod, but may not stack back as much as you'd like.

Thanks for the quick response-
I calculate the rod length to be 1.3 x (2 x 48 in. drapes)= 125 inches. There is ample room on either side of the window for the stackback, but as you mentioned, inverted pleats may not stack as tight, so maybe a little more length on the rod - 3-4 inches?
I am beginning to think maybe I should buy an inexpensive test rod, maybe 6 feet long and mount it temporarily to test one side of the drape and just see what happens. Then I could go from there.
Also- what are returns, ease, and pull? (Normally traversing draperies include returns and overlaps and some ease (so they don't pull), )
And how do the drapes mount to the rod? The ones I bought said they have hooks sewn in, but how are they attached to the rod? Do they hang below it, or slightly infront of it?

A return is the outer end of each drapery that goes to the wall, so there will be no light coming in at the ends and also so you can't see the window when looking in at the sides.
The overlap is an extra 3 or 4 " on the inner part of the drapery, so when they're closed, they "overlap" each other to keep light gaps out.
The ease is extra inches added on each drapery so when they're pulled closed, they pull comfortably without tightness.
If you're hanging them on a traverse rod, I'm assuming you want to be able to close these all the way. Hanging a longer rod for extra stackback may clear the window, but then you may not be able to close them all the way.
That's why I said you need to wait till they come to see what you get and you'll have to buy a rod to fit the draperies.
Traverse rods have carriers with holes in them, so you'll just put a hook into the holes. The top of the pin should be a half inch down from the top.