I considered a pistol-gripped Supernova a while ago too. In the end, I found that I didn't particularly care for a pistol-gripped shotgun, and bought a Winchester Defender instead. It has a standard stock and a factory 7-round magazine tube.
If I were you, I would go for something with a traditional stock, and something you can buy reasonably priced factory and aftermarket accessories for. That pretty much eliminates Benelli.
The benelli recoil pad is built like a hockey puck, and that will only be more apparent with a pistol grip. A replacement Benelli pad will run you at least $80.
I just bought a Limbsaver pad for my dad's/brother's Supernova at Sportsman's Warehouse, but it was more expensive than the rest. I'm not sure how well it works; we're putting it on this weekend.
It's also impossible to get a factory magazine tube extension. There are aftermarket extensions available, but I've never tried them.
I've heard that soldiers and police prefer a standard stock on their shotguns, partly because they shoulder more naturally, and also because it's easier to handle in a quick transition to hand-to-hand combat. I tried 3 different pistol grips on my shotguns, and I couldn't find a single one I liked.
I have nothing against Benelli or Supernovas, I bought one for my dad last Christmas and we use it a lot. Probably half the guns in our pheasant hunting group this weekend will be Benellis. But for a defense shotgun, I like my Winchester Defender. I got both of mine for under $200. In your position, I would also take a strong look at a new Remington 870 Police shotgun, or maybe a used 870 Wingmaster Police Shotgun. Even an 870 Express, with the factory magazine extension, would be an excellent choice.
And whatever you decide to buy, be sure to shoot it regularly.