"Kill Zones"
While one cannot cover all the windows and doors, it may be possible to direct those who are illegally entering your home into "kill zones" by limiting their choices of movement, directing them, in other words, to "stack up" in certain confined spaces or at a certain point - kind of a Thermopylae type defense, if you will. This reduces the effectiveness of the invaders' greater numbers, and puts them in a "kill zone." A hallway, or even the way the furniture is laid out, all these can become restrictive of movement and create a kill zone.
If you then pre-arrange for armored cover from which you can attack that kill zone, then it becomes very difficult for the attackers to get past that point, no matter how many there are (unless, of course, they use explosives, etc.) Drywall and wood paneling DO NOT stop bullets!
At the point where the kill zone is created, it is also good to create obstacles and distractions that will cause the attackers to stumble and fumble and to have to delay their advance, thus making them better targets and allowing you to get off more shots before they can react. Mirrors, manequins, something throw down on the floor that they won't see in the dark and thus stumble over, etc., all these are devices that can be employed. Be creative. How far you go depends on just how serious the situation is in your neighborhood, and the likelihood of an attack. Home invasions are becomming more common, so it is something to think about. Anything you do is likely better than doing nothing. Better to give it some thought and develop a plan.
The main idea is that at the point where you make your stand, you don't want to be caught in a crossfire, so you try and set things up to direct and control the movement options available to your adversary. There is almost always some point at which movement is restricted, such as hallways and stairs. A safe room employs the same idea, since you can effectively cover the door into that room as a choke point.
Another crucial aspect is having the TIME to react. You need perimeter alarms and entry alarms. Early detection of the threat will give you time to put your plan into action and for everyone to get to battle stations. Everyone should have a specific job and place to be. Family members wandering around in a panic during a home invasion crisis are not what you want to have! If you have that early detection, then eveyone can get to where they are supposed to be - hopefully.