Some things to note,
Great guns, but not the most economical ones, love the design, but if you just want something to bang around, there are cheaper guns that work, Mossburg et al.
The barrels on these shotguns are not necessarily interchangable, depending on age, some are "soldered" or permanately attached to recievers, and guns made before a certain date will not allow you to have additional barrels fitted, an issue if you "like me" have one that has an odd duck barrel that does not do all you want it to do. (in my case short with a cutts compensator).
If you just want to screw around with a shotgun an 870 is much more universal and available.
I personally prefer 2 3/4" chambered 12 gauges IN PUMP ACTION SHOTGUNS - for the simple reason that when you pump the slide, the pump has to travel a distance sufficient to "clear" the shotshell, in this case this distance must be atleast longer than the fired length of the hull, and it increases in shotguns manufactured to fire longer hulls, for instance I am just over 6' tall, with corresponding wingspan an Length of Pull, but 3.5" 12 gauge guns I feel are too long between trigger and foregrip, perhaps fine for shooting ducks and geese, but I cannot use them otherwise.
A 2.75" chambered gun however I can clear the shells much more easily, and indeed, this means the foregrip fits much more comfortably. This is less of an issue in autoloaders, and a non-issue in breakaction or single shot shotguns.
As to the autotrigger, my mother almost shot my father years ago due to this phenomenon. Keep the damned finger off the damned trigger, and always point the gun in a safe direction. Guns 101.