I don't know if this site has some weird legal disclaimer attached to it somewhere or if it's just that nobody here has ever actually tested armor but there is a little area that should be cleared up... NIJ ratings include a backface deformation standard. The vests themselves will often prevent penetration of a bullet but fail the backface deformation test. A LVL IIIA kevlar vest can, note I am not saying always will, but can keep a 5.56 from penetrating at suprisingly close range, like 25 yards even. It ends up looking more like a V.50 test. If you keep adding layers of kevlar yes, you will reach the point where you are stopping level III threats reliably. You can even stop a LVL IV threat if you have enough layers. The is no magic or voodoo involved here, make a big enough pile of anything and it will stop any bullet. You could stop a .50bmg SLAP round with marshmallows if you had enough of them.
The thing is kevlar isn't magic either. It's a good fabric that is useful for making armor but it possesses no magical property that makes it bullet resistant that is lacking in all other materials, it just has real mechanical properties. Somewhere not too far past LVL IIIA kevlar ceases to be cost, weight and bulk efficient and other materials like steel, ceramic and titanium are more efficient.
You would probably be perfectly fine with some really good LVL III protection which will stop pretty much any FMJ or hunting bullet you'll encounter. Metal plates are extremely durable and have awesome multi-hit performance. They are vulnerable to two specialized situations. One is very high velocity small caliber rounds, somewhere around 3500fps with less than .30cal projectile. It defeats the metal because it turns its kinnetic energy into a whole lot of heat on a small area and burns through. This is exactly why ceramic plates are able to stop these sorts of rounds actually. The other threat to metal is real AP, not just steel core like SS-109 or M43 but real AP with a hardened penetrator. Ceramic will stop that fast skinny stuff and it will stop AP if its rated for it. The downside is its multi-hit performance can't even come close to steel and the ceramic plates are much more easily dammaged. A solid thump can cause a non-visible crack that can compromise the protection in the effected area.
What makes the most sense to me would be to wear your standard kevlar vest all the time. It will protect you from a lot of stuff for not a lot of weight and bulk and if the bullet has to pass through something like a car or tree first it could very well be enough to defeat the threat. Then when you know you are going to be in a high threat situation you can put on a plate carrier for extra safety. Grab a helmet if you want to what the heck. If you are going to be wearing and removing and jostling around some plates in a carrier then you might very well want the durability advantge of metal plates. If you're going to wear the plates all the time wear what you want. There are polyethylene plates that are very light weight and give a LVL III+ rating but I have no idea how they'd handle the cold up where you are and they also have issues with stopping small caliber high velocity threats. Not to mention they cost a fortune.
I can definately understand your concern though. I am in a rural area and it is possible a thoughtless individual taking a bad shot at a deer could zing some lead over my way. Most people out here have a deer rifle or a shotgun so if anything bad ever did happen it'd be those threats I'd have to worry about. So much for the Fallujah theory. Of course if you ever shoot at public ranges I'm sure you've observed some very unsafe weapons handling as well. Realistically armor is a piece of safety gear that is appropriate to our sport just like eye and ear protection.
