As for taking a class, I always recommend training for anyone who keeps a gun for self defense. In fact I strongly recommend training beyond whatever minimum is required to get a CCW.
Being able to most effectively make use of a gun for self defense involves more than just marksmanship.
[1] You will want to know and understand the legal issues -- when the use of lethal force would be legally justified, when it would not be, and how to tell the difference. You will want to understand how to handle the legal aftermath of a violent encounter and how to articulate why, in a particular situation, you decided to take whatever action you did.
[2] You will want to know about levels of alertness and mental preparedness to take action. You will want to understand how to assess situations and make difficult decisions quickly under stress. You will want to know about the various stress induced physiological and psychological effects that you might face during and after a violent encounter.
[3] You will want to develop good practical proficiency with your gun. That includes practical marksmanship, i. e., being able to deploy your gun and get good hits quickly at various distances. It also includes skills such as moving and shooting, use of cover and concealment, reloading quickly, clearing malfunctions, and moving safely with a loaded gun.
Is all this really necessary? That will be up to you to decide for yourself. It will depend on your personal view of what you need to be able to do to believe yourself to be competent. But --
- If we wind up in a violent confrontation, we can't know ahead of time what will happen and how it will happen. And thus we can't know ahead of time what we will need to be able to do to solve our problem.
- If we find ourselves in a violent confrontation, we will respond with whatever skills we have available at the time. If all you know how to do is stand there and shoot, that will probably be what you'll do. It might be good enough, or it might not be.
- The more we can do, and the better we can do it, the more likely we'll be to be able to respond appropriately and effectively. The more we can do, and the better we can do it, the luckier we'll be.