In the online gun community, preparedness for every situation is well-discussed. People of course advocate carrying a gun, but many also advocate carrying spare ammo for the gun, a backup gun, and sometimes spare ammo for the backup. A high-quality assisted opening knife is also a must, plus several classes at elite gun training schools. All this is used to fight your way to your trunk or armored saferoom, where you keep a bug-out-bag that has a combat rifle with at least 15 fully loaded 30 round magazines, and supplies to live for several days.
If you take this sort of thing that seriously, you have not only crossed from prepared to paranoid, you are now spending your time preparing for disaster instead of living. If you are not law enforcement and there is any significant chance that you will need more than 15 rounds of ammo, you probably need to make some changes to your lifestyle. I'm not saying that everyone who trains hard is paranoid. If shooting is a hobby and training is part of that, it is no more paranoid than a race car driving school.
So what is enough?
A basic gun safety course, preferably with live fire--The NRA course that most Ohio CCW trainers use is a good start, although with 10 hours of classroom time, some extra should be covered. 2 hours range time is decent, if it isn't split with one instructor and 15 students.
You should have some training or practice in fast "close enough" shooting--have someone else signal when to start, and shoot 5 fast shots at a paper plate (or even better an IPSC target) at about 7 yards. If you miss the plate (or A zone) often, you are going too fast. If your shots are all centered in the plate, you are going too slow. Working with a shot timer is an added bonus--Time does funny things, and what feels like half speed may drastically improve accuracy with a minor increase in time. "You can't miss fast enough to win".
If you will carry, it makes sense to do some practice from the holster--This is hard to do with live ammo, because most ranges won't allow it. I really can't argue with that rule, there are lots of people who shouldn't draw and fire unsupervised. I'm lucky that my club range allows "known action shooters" to shoot from the holster. You can also get some benefit from practicing with an empty gun, or even better an airsoft or BB gun.
If you get a chance to shoot IPSC, IDPA or even Cowboy Action shooting, you will learn a lot in a few matches. These are sports designed aroudn scenerios--you will draw, fire and move around on the clock, and your score is based on time, with time added for poor accuracy.
Much beyond that should be considered only if it is fun--If it isn't enjoyable, you should look at other ways to improve your safety. For strict time and cost-effectiveness, I should get a car with airbags before I spend money on self-defense stuff--I've been in far more car accidents than violent assaults.