Well, the general length you are looking for would be based on your build and height. The scalps need to be proportionate to the rest of YOUR body, or they wont look right. I would suggest looking at fett pics on the ref. cd to see about where they fall lengthwise on him, then measure to that spot on your body. Hope that helps, and if it didnt make sense please feel free to PM me.
12"? I am referring to total length, end to end. They need to be long enough to go over your shoulder and down the other side, and then a little past your waist. 12" would be about enough to go from your waist to armpit on one side.
I've looked around a few crafts stores (Michael's, AC Moore, Joann's and Wal-Mart) and haven't been able to find long braid or unbraided hair. All I found was backs of short curls. Anyone know of an online supplier or website to get hair from? I was thinking about buying 3 different colored wigs at halloween and using those but ran out of money while working on my jedi costume.