Welcome aboard, Ron- hope you enjoy your stay here.
You picked yourself a good shotgun, with proper care it will outlast you and you can pass it along to one of your kids. But even a great shotgun is not a talisman against evil, nor is it a magic wand. It is only a tool, and has to be _used_ by a willing and capable operator to be effective in a protective role. And you can't count too much on the mere sound of its action shucking to rout bad guys. These days too many of them are living with so much chemical enhancement, or the voices in their heads are shouting so loud, that extraneous sounds- even potentially lethal ones- just don't get through.
Chances are good you will not ever have to employ your Mossberg for its intended purpose. But should you ever have to do so, you need to have transformed yourself into a person who has at least the basic capabilities necessary to fight with a shotgun before the real need for those skills arises. I believe there is no better defensive tool available than a good shotgun and that is why there are several of them here at Chez Lapin. But it takes knowing how to shoot a shotgun at an instinctive level, plus knowing some basic tactics, plus having workable plans for home defense in order to employ your shotgun adequately in the home. Having a shotgun is only part of the solution, having the ability to use it well and a plan that enables you to use it so it is only a danger to BGs (the bad guys) is also very important.
I am not one of those who advocates going out of your bedroom trying to juggle a righteous attitude, a flashlight, a phone and a shotgun while looking for whatever caused that bump in the night. I strongly suggest working out a plan where you can hunker down with your family all together in a defensible place, behind good cover, with the shotgun between you and a backlit doorway- and anything that tries to come through that doorway. I don't know the architecture of your house or what considerations you have to contend with. But you should be able to work something out so you can gather everyone up and get them and you behind cover in a room where you can control the only entrance wih your back protected in case someone gains entry to your home.
Do you have an alarm system? A family dog? How many entrances from the outside and how easy to get through for someone who wants in? Do you have peepholes or cameras so you can see what's on the other side of the door? Doors good and solidly locked all the time except when in use? Do you live in 'condition yellow' and pay attention to what's going on around you, or are you often surprised by people coming up on you in public places?
Does your family practice fire drills? If you can incorporate the same plan to cover two purposes as far as the inside-the-house part is concerned, that will help simplify things a lot. That way in an emergency you, your spouse and the kids all know what to do no matter what, so far as activities inside the house are concerned.
As to choosing ammunition, I suggest that once you have a plan in place and can be reasonably sure you have everyone accounted for that you can find a way to feel more at ease if it is necessary to fire a load of buckshot inside the confines of your home. When you establish your plan you will also be establishing 'lanes of fire' with definite boundaries. You can arrange things so there is substantial furniture (bookshelves, etc) between the ends of those lanes and the rest of the house. Note that it doesn't matter which side of a wall at the end of your lane this ballistic barrier occupies.
Buckshot fired roughly parallel to almost any wall is very likely to 'skip' off the surface and continue roughly on its course parallel to the wall (they teach people who clear rooms as part of a team not to hug the walls for this reason). The walls will funnel projectiles toward the end of your lanes, the door will funnel the BGs toward your position if they are moving through the house. Your fields of fire will be deliberately limited, and if you have your family gathered with you so you know where they are, where you shoot is only something the BGs will need to worry about anyway.
Teamwork is a help in this sort of situation, one adult can cover the door with the shotgun from behind cover while the other is on the phone with the authorities and keeping the children under cover. I suggest having a cell phone as part of the plan, sometimes BGs cut phone lines on the way in.
I know this is more than you asked, but it is still all part of the answer. Look for some training opportunities around you- NRA instructors offer home and personal protection firearms training in many areas, just go to the NRA website at
http://www.nrahq.org/education/training/basictraining.asp .
Stay safe,
lpl/nc
edited to add: see the thread at
http://www.thehighroad.org/showthread.php?t=173868