Hi PiousPoet, and welcome Sandrala!
The yarn I use in the videos is just a cheap acrylic that I thought would be smooth-looking, and easy to see the stitches with. I tried using wool, which I prefer working with, but it was too fuzzy. A nice merino probably would have been the way to go! But I just used what I had on-hand.
For chain selvege, you slip the first stitch, and work the last stitch normally. Some people will always knit, or always purl, the last stitch, and always slip the first stitch the same way (k-wise or purl-wise). The difference created is nominal. I'm in the habit of working the last stitch as normal for the row, and then on knit rows slipping k-wise, and on purl rows slipping p-wise. Really, whatever you end up doing will be fine, because it's hard to tell the difference. But definitely do knit or purl the last stitch. Otherwise it would never get worked, and you'd be in trouble!