Less than one skein of yarn needed, or two skeins if you’re using two colors.

Gague:

4 hdc = 1 in.
About 3 1/2 rows = 1 in.

These will also fit a DS or a DSi, I can’t say for sure if they would fit the original DS, I don’t own one, but they’re a bit bulkier so these may be a bit too small.