From what I understand, it depends on your native soil. My sandy soil works well to just tamp the post to set it. I also went 4 or so feet deep with the posts. I did the same with a hops trellis and there was no issues.
I’m cane pruning all mine ans using the four arm kniffin. Either that or the umbrella kniffin if I have some that are more vigorous.
I did add one more wire about 18" off the ground for my irrigation line. It made trimming the grass much easier.