I believe that specialty archery calls the peep lenses for the hunting setups "verifiers" and the ones for the target peeps "clarifiers"
The verifiers are really just the lens in the screw in peep housing.
The clarifiers are the lens AND a stopped down aperture.
With respect to the power required, everyones mileage varies with respect to that. For some a #5 verifier will work just fine, and for others they may need a #6 or #7 (5=lowest power, 9= highest power).
The only way to tell is to try some of them out, but I would advise to use the lowest power lens combo you feel comfortable with. The higher the magnification of the lens, the less light it will pass and the darker your image will look. Possibly not such a big deal on the 3D course, but could be a 20 minute difference in shooting light at sunrise and sunset.
Now in regards to your main lens, you are certainly the one who makes the ultimate decision as to what works for you, but a 6X lens is awfully powerful for a hunting situation. I think for hunting I wouldn't go with anything more than a 3X.
Just as a data point, my indoor target rig has an 8X lens and #2 clarifier. At 20 yards I don't see any more than the gold center of a vegas face target. That is a spot roughly 3 1/2" in diameter. If I drew back on a deer with that magnification I don't think I would be able to tell which end of the deer I was looking at.