Hey -- so you did end up with andean treasure after all -- great choice! (I thought the others had convinced you to go for panache.)
I'd do at least two strands. I've done that with that yarn before and gotten a gauge of about 4 stitches per inch in stockinette, which is about the same gauge as the yarn in the pattern (according to yarndex). How does that sound? If you decide to go with that, based on my gauge, the stats of the yarn from the original pattern, and a little fudge factor for good measure, I estimate that 3 balls would yield a scarf that is somewhere between double and triple the length. So you might want to get 4 to be on the safe side. Better to have extra than not enough.
If you want to do more than two strands, let me know and I'll help you figure out the yardage. The more strands you use, the thicker it will be and the faster it will knit up, but the more yarn it will take.