A small pattern for drapes. You can mix patterns as long as they differ in size

Absolutely, yes.

I'd look for a something with that stylized leaf sprig in grey and white, or a grey and white small-scale suzani

https://www.fabric.com/buy/uk-731/premier-prints-suzani-twill-storm-grey

Something like one of these may be pretty. Hard to tell in regards to scale

Ooooh, I like those. Is that just fabric or actual curtains?

You can find ready-made panels in so many places, but here is a quick look at overstock.com. The thing to remember if you want the drapes to close the panels need to be 1 1/2 to 2 times the width of the window. Another alternative is to have someone sew panels for you . Seamstresses can be found on etsy who make drapes.

http://www.overstock.com/Home-Garden/Curtains/6420/subcat.html#qvclosed

It's just fabric but available at Joann's and they often have a 40% off sale. Pick your fabric and have them made. Etsy has people who will make them or even have them ready made in some great fabrics. I found this one also which I think is real pretty too.

Or check out West Elm, 39.00/long panel.

There are others, too.

Think scale and pattern....dots, geometrics, florals, stripes...small and large....you can mix them all so long as something is different, so small dots and small florals are ok, or small stripes with large stripes are ok, or large geometric with small dots, or large floral with large stripes, etc. Use colors precisely to unite them.

Sarah Richardson is a master of mixing patterns...

I definitely think you can do two patterns. But, I personally would do some pillows out of the same fabric that you use for the drapery for a little continuity.