How heavy is the bow, draw weight I mean. Up to 50# of draw, I would use 10 strands of B50, 12 strands for up to 65#.
The general rule of thumb is to provide 4 times the draw weight of the bow in bow string material. For example if you were using 12 lb test, you would need 17 strands for a 50 lb bow. Fishing line may have too much stretch, though.
Send me a Private Message and I can spool up some B50 to send to you.