One ball is JUST enough to finish this project as written. I ended up with 8-10 feet (at most) leftover, which I cut in to four equal lengths and used as a tie. If you a) would like to make a matching I-cord tie, b) have a burning desire to keep your gauge swatch, or c) are otherwise uncomfortable with that little room for error, pick up two skeins, preferably from a LYS with a return policy for unused balls. If you want to make several, purchase one ball per bag, and then get one extra ball for good measure. The pattern could also easily be reversed and worked from the bottom up so that you could simply stop when you’re nearly out of yarn.

Gauge is not crucial, as the finished product will stretch considerably in all directions, but if you are knitting too loosely you will risk running out of yarn.