<font color='#000000'>Can't answer #1 and #3, (well, I think the answers to #3 are "usually polyester fiber, and it depends") but as for #2, yes. The brands they carry like Vifa, Morel, Audax and Peerless are used by many reputable manufacturers including high-end. Their own Dayton brand can be good too, I've heard.
I'm not a hardcore DIY speaker builder/designer, though. But the Vifa drivers spec'd by Siegfried Linkwitz for his dipole design that I built came from PE, as did most of the crossover components.</font>