Use whatever size shoots well for you. Longer fletching or vanes provide more stabilization than shorter. Feather fletching provides more stabilization than plastic, but is more prone to damage/weather. I used to shoot 5" feathers from my compound, and still do from my recurves, but some tuning, a new rest & release and I'm now getting the same accuracy from 4" plastic vanes. I recomend you use a jig that will give you a slight offset as this will provide spin for the arrow. If you get right wing feathers you need to use a right helix , or offset.
