RE: new to fletching......
You made no mention of what style rest you are shooting with.
If you are shooting a drop away or a WB type rest then yes you can use a full helical and I reccomend it.
If you are using a two prong rest then you would not want a full helical as you will get major fletching contact with the rest. At the most you would only want a few degrees offset and that would be done with a straight clamp.
As far as shaft diameter goes it makes no difference at all. You just have to adjust the jig and clamp for the different shaft diamaters.