Quality of hackle is nowhere near as important as barb length of hackle, which should be about the same as the distance from the eye to the hookpoint. Three or four turns will be enough for a top-quality hackle with a high-density barb count. Up to six turns may be needed for hackles with a lower barb count. It’s important to remember that the hackle floats the fly, not the post, which is only there to wrap the hackle around. On that basis, use anything that will do the job. Cheap poly yarn is just fine. I like to tie my posts on the slim side, and crop them short, but others like to use them as a sighting aid, and leave them longer, and even use different colours for different lighting situations. Tying off the hackle can be tricky. Watch videos on Youtube and pick the method that suits you best.