Yes, you cast off first then fringe. When you get to the fringe we can help you. It's easy to do.
It doesn't matter if it's best quality yarn. It's all a matter of perception anyway. I started with discount store yarn and as I got better I bought higher quality. There's still a place for less expensive yarns though. Lots of people still use them and that's fine. You use what you can afford and what you like to knit with.