Your question is a VERY good one, but if I answer only your questions it will be too personal, as many others have other calibers, and most important the uses one has for a gun determine what is needed to make the gun versatile.
For example, the 22 rimfire is incredibly versitile if one plays with the very broad spectrum of ammo available. Velocitor LR hp's by CCI make it suitable for everyting from small game up to knocking 1400 pound beef down. Very low report ammo is available etc, etc.
If the same approach is used for whatever calibers one has at present, and loads, bullets are selected to suit the individual desires, one can live very comfortable with just one handgun, one rifle and one shotgun.
To personalize my answer a bit more. -- You don't need a supercharged 45 to do what you want. The ACP loaded to max with an LBT LFN will do all that can be done on man or beast and be comfortable too shoot if you place your shots well. If you don't do that, more power behind a bullet won't save the situation, or if you miss, a cannon isn't big enough. So I reccomend for everyone be sure you can accurately place the bullets of whatever you choose to shoot, then be sure the bullet and load you choose delivers the most kill with the power available. So I's say stick with your 45 becaue you have it, like to shoot it, and your main thrust is teaching defense. You probably won't want a 44 revolver for that purpose.
I personally trust a double action revolver much more than any auto, because tripping the hammer after a misfire gets the missfire out of the way. but that's a personal thing.
I like your rifle / shotgun choices. A lot of moose are killed with the 308 and many alaskans like a 12 guage loaded with 00 buck or slugs for problem brown bears. Both will work fine on everything down to mice and grasshoppers. But above all, I like guns which, should I drive off into timbucktwo and find I've left my ammo behind, I'll be albe to walk into a local hardware store and pick up a box of something that will go bang and kill what I'm hunting for.