I would make my own bedroom the "fortified" one, simply because that's the one I spend the most time in and the one that I "control." Train your kids to run to your room when trouble is afoot, or grab 'em yourself if they're too young.
If you're serious about fortifying it, use an exterior door and reinforce both the hinge side and the lock side as well as the lock strike. You can find lots written about that on the net.
Keeping a "throw" key to your exterior doors in the bedroom is such a good idea I'm surprised more people haven't caught on. My advice is to tie the key to a short length of broom or rake handle that's been painted da-glo orange... easier to throw and easier for the cavalry to see once it's thrown.
Remember the shortfalls of the 911 system with respect to cell phones... do not assume that they will immediately know which address to respond to. Give your address twice - that's more important that your name! If time allows, describe what you, the homeowner, look like and what you're wearing.
I'm happy to hear you're looking well past just having a gun on hand. The mind is the weapon, the gun is just a tool.