Questions such as the OP's always seem to me to require writing a book to fully answer. But, to be brief, I use a Mossberg 500 Persuader 18 1/2 inch barrel - 7 rounds in the mag tube, chamber empty, safety OFF, and the trigger PULLED. With the trigger pulled I do not need to finger the slide release to pump the weapon. That way when I'm awaken at 3am from a sound sleep, I only need to remember to pump the weapon and I'm ready! I use 00 buck. I plan to mount a light so as to be able to see who to shoot. I have 200 lumen lights but am thinking of going with something in the 50 lumen range because I have tried using the 200 lumen at night, with some outside light coming in the windows from streetlights, etc and I find the 200 lumen light can even give me some momentary night blindness (not good!!). Maybe a laser would be nice too to make sure I hit where I want in a moment of high stress - 00 buck will go thru inside
and outside wall in many newer homes. It will be bad enough if you shoot a BG, but if you also hit your neighbors house it will be even worse. Remember, it is against the law to shoot anyone - even a BG - however you will use the defense of 'home defense' in protecting you and your family (keep a criminal defense attorney's phone number in your wallet and don't talk to the police w/o your attorney present !!!)
NMduckslayer makes a good point:
it's not really considered to be a good idea to go roaming through your house with a loaded shotgun in the middle of the night if you suspect that there is an intruder. It's better to stay in your room with the door closed and wait for the police to clear the house unless you have to go get your kids out of their room(s) and bring them back to your room and then wait with the door closed for the police to arrive and clear the house. It is refered to as home defense and not home tactical room clearing for a reason.
That being said, a whole lot of new homes only have hollow core PVC doors between rooms, and, many have split room designs. My new house has the master BR on one side and the guest BRs on the other side. The front door opens to a open dining rooms and a great room with the MBR door right off the dining room (no hall). I should probably replace the inside doors with something solid - harder for a BG to kick in. A good defendable area could be behind the bed looking toward the BR door kneeling down with the gun resting on the bed - and with a phone on that side of the bed.
As also suggested, what ever you buy, get a couple of boxes of birdshot at Walmart and practice with your new gun. Practice at the shortest and at the longest distance you might need to shoot at in your house. Then buy a couple of boxes of 00 buck and practice with some BG full size targets and pick the brand of shotshell that patterns best for your gun at the distance you figure you might be shooting from.
Finally, in a 7 round magazine, those 7 round add weight to the front of the gun - load only 5 rounds and see what a difference in weight it makes. So, everything you add on to your gun makes it weight more - just be aware. If you're young, maybe that won't make much difference
If this is truly for HD, it will probably be a one time buy and hopefully a '0' time use (other than practice) so buy something that fits you and feels good when you shoulder it. Inexpensive - vs - expensive - vs - used (and checked by a gunsmith) means less than something that feels good at your shoulder.
Robert