You will have no problem pounding the posts in they way they currently are, I have put in many of them straight out of the woods. Let them sit a few months and the bark becomes loose and when you start driving them the bark comes off, the posts go in better if you turn them upside down. My dad has told me if you put them up in the orientation as they were standing in the woods and the bark is left on them they will grow, I can tell you that yes spruots of limbs may start but they will also start on ones put in upside down with the bark still on them. 2-4D in your fence spray mixture will take care of that issue.
I have sawn some of them and used them for lumber, the wood is very hard and tough to work with. IF your sawyer can read the log as he is cutting then yes you can get a squared post that will be structurally sound. My experience with Locust is the tree don't usually get real big diameter and on occasion you may get 6x6's 10' long, more common for a true 4x4 8' long, but if the sawyer can't read the log right you can get something that will warp/bend/bow within a month of sunlight.
I have also taken my cut to length posts and split them lengthwise. This is not as hard as it may seem and with two axes you can work through a small pile fairly quickly and double your post count. You can end up with a post that was 6" round on the small end and have two posts that are 3" half rounds on the small end, makes for a pretty good post.
When driving them I will add don't stand in the path the pieces and parts of the tree/post will go if it blows out.
I have also augered a hole and set them, works as well as anything else. I have not augered a hole and drove a post, I would like to get a 2" auger for my gas powered auger just for doing that in hard ground. Cutting a wedge or pencil point on the bigger posts helps, isn't always required and in my experience doesn't make anything less stable. If they aren't cut symmetric they will drive crooked. I could take you on a walk around our farm and everyone within a mile and show you miles of old locust fence posts that were there as far back as my dad can remember that were cut and dug and packed in the ground the same day.
