You add 10% for take up no matter what kind of material you are using, because once you take it off the loom and it is no longer under tension it will shrink. Plus if you are using Cotton or wool you would add another 10% for shrinkage. If you want fringe I wouldn't zig zag it I would either do the twisted fringe or hem stitch it(you do this stitch while it is still on the loom), or you could also just take a certain number of ends and tie them in a knot.
No problem helping. I am not very good at describing things so I hope I am making myself clear. I wish I could show you rather than trying to write it.