RE: Fletching: Offset vs. Helical
As stated above, helical will provide the most drag to the back of the arrow and will stabilize a broadhead better than just about anything else out there. That extra drag does not come without some compromose and that is long distance velocity. Out to abouit 35 yards or so, you will not be able to really tell the difference between offset and helical. Beyond 35, the helical will drop faster.
For the amount of helical, generally the clamp on your jig sets the amount and is not adjustable. For my helical fletches I also put on as much offset as I can and still keep the base of the fletch (feather or vane) in full contact with the arrow shaft. Let that be your guide as to when you have too much offset.
With respect to the jig, there are many good ones out there, but my personal favorite is a Bitzenberger. Somewhat pricey when compared to other jigs, but it is a joy to use.