"I am ordering new strings and would like to know how to tell how many strands I need. I have a bear Kodiak Hunter. 55" string I am going with a B50 dacron."
Depends on the draw weight. 12 strands for up to 40-45#, 14 strands for up to 55#, 16 strands for over 55#.
"Another question is what is the real diffrence between B50 and fast flight strings."
Most any FF type string is much more durable, has much less stretch, much less creep, much less vibration, and you may get a small increase in performance.
I wouldn't suggest a FF type string on a non-FF bow. I've never seen evidence or had any proof presented that shows damage to a bow from a properly made FF string and a bow with the string grooves cut at the proper angle...but I still wouldn't risk it.
Chad