To answer your questions:
1.) Most people use a gopro because it is rugged, has an outer shell that protects the cam from the elements, and it shoots a pretty good video
Contour HD, ect will also work, but GoPro made a name for themselves, and the "Pros" love using them for SPECIFIC POV (point of view)
When you are watching a snowboarding DVD or movie back in the day, they are using high quality dedicated video cameras in specially built housing for the camera to protect against the elements. What you don't know is that the cost of those cameras were insane. Nowadays, you can get a Digital SLR with video capabilities, get a good lens on it, and you can really get some impressive shots... From personal Experiences learned however, Riding with a Digital SLR is not the smartest of things to do, as they dont take falls very well.
2 & 4.) Having someone ride behind/in front/side are all good angles. By doing multiple runs, we can edit and anayalze from multiple angles to critique your riding.
The pole you are referring to can be a monopod attached with the camera mount or, as a DIY project, you can size a metal broomstick from your local dollar store, cut it to fit, and then attach the camera mount to the other end of it. Simple search of google can provide DIY instructions.
3.) A good mixture of both. Show that you have the basics down first, then start to incorporate the more difficult tricks/tasks. Dont forget to get dynamic!
Hope this helps!