We have a guy (one) that I like at our WalMart. Good guy and knows the guns, a veteran too, served in VietNam. We also have a small local place, real good folks, like family!
Other than that, your likely to find more useful applied knowledge without any BS or bias here or on the sister sites. Hopefully you can find a local place thats cool though!!!
Sounds like youre narrowing the field some!
With the chokes, Mossbergs accuchoke set is a good deal. For whatever reason, the combo sets from Mossberg are just real good deals, if its a second field barrel or choke sets or home security barrel... the mark up from the gun to the gun + combo is worth the price when you begin to compare purchasing each thing individually.
I know you had said before you arent particularly recoil sensitive. The 12 ga. I think offers more choices with ammo and the cost is generally less because it is the most used gauge of shotgun. You'll also have access to loads like Federal Premium's VitalShok with TruBall if you dont decide on a rifled barrel. .410 ammo can be stupid expensive and my daughter likes to eat it up! Shes gettin a 20 soon! Maybe even an SA-20! I dunno she confuses me by goin back and forth, but I think shes diggin the SA-20 with 24" barrel and 13" LOP stock! My feelings, if youre ok with recoil, go 12 ga.
Heres somethin of interest about the Mossberg autoloaders. While many other makers boast having the softest shooting auto's, but because of Mossbergs gas blowback system, its said to be much softer than say the inertia or recoil operated guns. Mossberg isnt real good at advertising and boasting the things they do well...
Back to the LOP... Something you can do to get an idea for the LOP that may work, measure the length of your forearm. Bend your arm on your dominant side, roughly 90 degrees. Measure back from the first joint of your index finger to the bend in your arm, like to your bicep. Its not a perfect science, but should give an indication of what will work.
Something I mentioned elsewhere when considering hunting in cooler if not cold weather, is that adding heavier clothing will affect LOP. I keep a 12" LOP on my 590A1.
In summary;
12 ga. if recoil isnt an issue, it offers more load choices and can generally be less expensive to shoot
LOP, get your hands on a few different makes and models to see what fits
Combo sets to get barrels and possibly choke sets to meet your needs, like maybe a rifled slug barrel for deer, (though deer can be hunted with Foster type rifled slugs from a cylinder bore barrel) and maybe a field barrel with interchangable choke tubes
Or maybe a 12 ga with a single field barrel and choke set
I think thats all I got for now.