OK, I'm gonna take a stab at the how much is enough or too much question..the answer is kinda esoteric though.
The answer to how much training is enough (IMHO), is when your skill level is such that should you find yourself in the most dangerous situation you are likely to encounter, more training wouldn't give you better odds of survival. In other words, if you get killed, there was nothing you could have done differently with more training.
Of course we can never truly know what that is, like driving a car. Your car has a very defined performance envelope at any given moment defined by the vehicle, tires, and road conditions. You can't know it exactly, but if you exceed it you'll spin out of control.
Let’s just look at home defense and skip physical security measures (whatever they are, the bad guys still got in). So, evaluate the realistic threat level and the realistic "most dangerous" enemy course of action. A highly trained militia group raiding your home with flash-bangs and night vision at 0400 is not realistic.
However, I'd posit that multiple armed criminals kicking in your door intent on beating, raping, then stealing your stuff (and not just running at the sight of a gun) is realistic "most dangerous" threat. We have seen this happen multiple times from the ghetto to very high end homes in high profile cases. Odds...miniscule, but we aren't looking at odds of it happening, just the possibility.
How much training do you need to handle multiple armed threats in your house, such that if they kill you, more training wouldn't have mattered?
I'd say you need enough training to get to an unconscious level of competence in hitting the vitals in low light while you (and they) are moving, 10yds and under, and fast under stress. You need to be able to transition to multiple targets. You need to have trained to shoot until the threat is eliminated, not shoot 2 and assess.
You need to have enough H2H training that you will not hesitate to close and strike if your gun is empty or jams (clearing a malfunction or reloading is a recipe for disaster at room-distance.) Your strikes need to cause injuries, feel free to use the firearm to strike. You must train to seamlessly transition from shooting to striking with the firearm. As an aside, a muzzle punch to the throat or sternum with a carbine, shotgun or handgun will be lethal (very, very high probability) with your body weight behind it…even if you just weigh 100 lbs.
You need to know how to use light and cover. You need to know how to search a structure if you have no choice and have to go after a family member (if you live alone, I guess you don’t). You need to know basic immediate trauma aid, lest you all survive the gunfight only to have someone die when immediate trauma first aid training would have saved them.
I’m forming my thoughts a lot as I type. I guess there is a pretty big gulf between a reasonable “minimum” and getting to the level where more training wouldn’t matter even in the realistic worse-case.
I also just realized, I do probably have enough formal training to handle the worse case where more wouldn’t matter. However, I don’t practice all of those skills enough, so there is room for me to get killed due to not executing what I know well enough. That I need to have the self-discipline to fix…I can do it almost all for free via dry-fire.
Edit: I lied, I could definitely use more force on force training to stress inoculate the skills I have.