Pete,
I have the same scattergun as you: Mossy 500, 18" barrel. It's set up as follows:
Synthetic stock and forend (both with pistol grips) from Choate Tool. Contrary to the experience of others here (that's just me, contrary as a hog on ice skates), I find accuracy is no problem. I shoot clay with my rig, and average 84%.
An additional benefit of the PG stuff is the final appearance of the gun. If I were a bad guy, I'd likely die of fright just looking at it.
At home, I load it with 6 Sellier & Bellot #00 shells in the chamber and magazine. The sidesaddle has 4 #00 and 2 Winchester rifled slugs. I figger if I hit a goblin with 10 charges of #00 and he's still coming, the slugs should finish him. If not, I'll throw the gun at him and run the other way.
Overpenetration from #00 and slugs isn't a (big) concern for me, and I don't have a problem with recoil from max dr loads, having gotten used to it on the range.
Regarding lights: y'ever tried to use the Harries technique with a long gun? Doesn't work real well. I have a Surefire light mounted on the magazine. Covering friendlies with the muzzle isn't a factor as I live alone.
As always, YMMV.
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"America is at that awkward stage.
It's too late to work within the system,
but too early to start shooting the bastards."
--Claire Wolfe