That birdshot will defend you quite well out to 50 feet or so. Beyond that you’d need some buckshot (#4 is fine) or slugs. Slugs will drop a bad guy out to 150 yards or so with a bit of practice.
Yes, the 500 will safely chamber and fire 2-1/2 or 3 inch shells. But trust me, 3 inch in any configuration has a hell of a kick.
Now get thee to a gun range and practice. Without it all you have is an expensive and poorly designed club. Don’t believe the myth that all you have to do is point a shotgun in the general direction of the bad guy. Accuracy counts just like any other firearm.
But you have bought well. The 500 is a rock solid design that will serve you well for decades to come if you care for it properly. I have one and I absolutely love it.
Good luck.
L
I agree on aiming - at most indoors distances, the shot patter will not expand more than the palm of your hand. A casual point and shoot is not reliable.
For a full stock, I like the shoulder mount, and don’t use anything else. Pull it snug and let fly.
Some would suggest taking my advise on such things may be less sound, my fowlers, 12 and 10 ga. are caplocks, and one small bore cape gun, .32 cal and 12 ga cylinder bore in flintlock. It’s been years since I’ve fired borrowed breech loaders! ;)