Rip-stop nylon works best if you cut it with a pencil point soldering iron. It will cut the fabric and then melt the threads back so that they don't fray any. Much like taking a match to end of a nylon rope.
When you look at the white hem it is folded over and has 2 sides. The slit in the hem is cut only on 1 side of the hem, near the bottom and on the mast side of the sheet eye. The slit is only about 1/4 long - just enough to slip in the batten.
It is just a matter of puffing out the hem - so that it is more 3D and not flat and touching the iron tip to just one side of the hem to make a small incision.
Anyplace that sells stunt kites should carry an assortment of the graphite rods. Or hunting stores that sell arrow shafts, tips ect. Or just use the plastic rod you were going to use. The graphite rod I use is very strong, light and has very little bend
The pic shows an arrow nock on the end of the graphite rod to make insertion easier. The rods come in 3' lengths so I cut 2 to 26" and used an internal ferrell in the middle.
Works well for all points of sail.
Hope this helps