I took a tactical shotgun course from Bill Davison at Tac Pro Shooting Center. I bought an 870 Express, and tricked it out with a rifle sighted barrel, a Knoxx Spec Ops Stock, Choate forearm and sling. The gun came with an 18.5" bead sighted barrel, and a factory +2 extension. All I needed was the shotgun. The rifle sighted barrel was nice for slug work, but not necessary and the magazine extension was nice, but not necessary. Ok, we shot plate racks with bird shot, and without the extension, I would have had to load an additional round to get the 6th plate, but guess what...reloading is largely what it is all about.
Point I am getting to is that you will be fine with a plain stock Remington 870 Express Home Defense shotgun, or pretty much any reliable shotgun. I would prefer a pump. Your Benelli is fine, and you really don't need the pistol grip. If I had it to do over I would not have spent the money on the Knoxx stock, but would have opted for a Limbsaver pad on the original synthetic stock.
Learning the tactical shotgun is far less about the shotgun than you learning to manipulate and operate in effectively, whatever it is.
