I want to find out if I book in advance from the web, do I pick up the tickets when I land in Japan, or it is not necessary.I am not familiar with their online reservation system. Do they not explain it?
I also want to know if this is a good way to go to kamikochi in terms of convenience and cost.
Yes. But there seems to be only one per day. If it is not suitable to you, I recommend to travel via Matsumoto:
http://www.japan-guide.com/e/e6040.html