1. On my Remington 870P, I have a Surefire forend light. I like the feel of the shotgun better, without the light. With the light, and a 2 round mag-extension, the gun doesn't swing as quickly as I'd like. However, if it's dark, I can be lighting up a threat and perhaps blinding that threat, too.
But if it's your only shotgun, you may not have the luxury of deciding if your gunfight will occur in lightness or darkness. I suppose you could constantly remove and install the forend when it gets dark, each day...
2. The light is another item to maintain. Be sure the batteries & bulb work. Of course, each time one tests the light, the batteries drain and the bulb could blow. "Murphy's Law" would have the Surefire forend's light malfunction just when one needs it. Perhaps a backup flashlight in one's pocket would be a good thing.
3. The Side-Saddle products are a good thing. In fact, I still need to buy 2 more Side-saddles for my other shotguns. The shotgun is limited in available ammo capacity and more ammo is a good thing. Right now, I compromised and bought a 4-round Side-saddle. If you get the 6-round version (although there's the Mesa Tactical brand which comes with even more round capacity), be sure you have a short-type forend for clearance. The Surefire forend light is already short enough.
I also use shotguns with the Speedfeed stocks with the built-in ammo holders as well as shotguns with butt-cuffs to hold extra ammo. I prefer the Side-saddles for balance and ease of pulling the round for loading into the gun. For me, I don't like the Speedfeed stocks as I find the standard 14"+ length a bit too long for me.