A short barrel is an advantage indoors. A high-quality magazine extension is not a bad idea, and while you are at it, make sure the magazine spring and follower are of high quality, too. Not much point in adding something that gives you more rounds, if those rounds won't feed.
A light is a mixed blessing, and not as vital as some make it out to be. It depends on how much ambient light you will typically have. Ghost-ring sights are another mixed blessing. At home defense distance, a bead sight is adequate, and it may well be the fastest to use. (We all have different eyesight; what works for me may work otherwise for you.) A bigger/brighter/tritium bead may be a very good idea.
I like the Vang-comp big-head safety.
One of my duty/HD/SD shotguns is a very plain-jane parkerized 870P. I added a Vang-comp barrel to get smaller buckshot patterns at distance, when patrolling the streets, and the barrel wears a plain bead. I added the Vang big-head safety button, too. No magazine extension.
My other 870 is a custom from Scattergun Technologies. Ghost ring front sight, tritium front sight, Vang-comped barrel + porting, threaded for choke tubes/breacher attachment, big-head safety, mag extension, sling mounts, custom black finish, the works. I bought it to use as a designated slug gun for policin', not really for HD. It could certainly do double duty for HD, of course.
Know which shotgun I actually like the best? The basic, bead-sight, parkerized 870P, of course. Basic is good.