For home defense I'd have a barrel 18-20 inches in length - 12 or 20 gauge.
As for a rifled barrel and buckshot, why not?
The rifling and centrifical force of the spinning load will make it spread out faster, giving a wider pattern in the short range one would be using it in a home.
I've set up several 12 gauge pumpguns for home defense, with the M1200 or M870 all.
For an exclusive home defense shotgun, I'd use an 18 1/4" barrel (the NFA '34 federal gun law requires that shotgun barrels can be not shorter than 18 inches).
Also the shorter the better, with a stock of course. With a youth-size gunstock, a shotgun with 18 1/4" barrel would be @36" long - and plenty nimble and manueverable in a tight hallway.
I would have an extended 7-shot mag on that gun, and possibly a light I could turn on and off with my trigger hand. No need IMO to have other accessories except a side saddle or elastic bandolier to reload with.
During high school back in the seventies, I hunted deer [and black bear] in N.W. Florida with the 12 and 20 gauge. Helped carry out a smallish adult bear killed with #1B from a Browning Sweet 16 Auto-5 SG. I never killed anything while living in Florida, but years later I killed two mule deer with #4B at 40-50 yards.
BUCKSHOT WORKS!
Provided your particular gun and barrel will pattern it well.
For home defense, a standard trap load with 7 1/2 shot will easily penetrate an intruder's carotid artery at most ranges. Certainly with a medium field load of sixes or fours.
Whatever you use, consider using a shell with a moderate to low velocity so you can recover quickly for follow-up shots.
A slug might be useful if you had to shoot through walls or furniture a BG was using for cover ...... if necessary.
Two books I found extremely useful were;
Tony Lesce's "The Shotgun In Combat" and
Gabrial Suarez's "The Tactical Shotgun."
Lesce spent a lot of time discussing loads for inside defense, including what will and won't over-penetrate sheetrock or regular walls. Lesce is who recommended the 7 1/2's as adequate for defense.
Suarez is an LEO, and recommended using the old-style PolyChoke for shooting slugs and buckshot, and also a bunjicord for use a sling when the gun needs to "be close."
I also strongly urge consideration using a 20 gauge over a 12 gauge if one has a wife or children who might need to use the weapon, to better handle the recoil and recover for follow-up shots. Plus 1-ounce #7 1/2 birdshot loads in the 20 gagg are plenty stout, but if not the 20 pellets in a #3Buck pattern should be.
FWIW. Luck!