Bwannabe,
I think your idea of the HD SG is excellent. Yes, you can put too much stuff on a gun. The key to accessorising your gun is knowing its mission. For HD I have mine set up similar to yours except that I have a +2 mag tube extension. The tube is kept loaded down by one round so that in the event I have to select-load a slug all that is required is to feed the slug into the tube and rack the action. If an ammo change isn't required then it's easy enough to top off the tube from the side saddle. Right now I keep two buck and two slugs on the saddle.
I think your idea of the HD SG is excellent. Yes, you can put too much stuff on a gun. The key to accessorising your gun is knowing its mission. For HD I have mine set up similar to yours except that I have a +2 mag tube extension. The tube is kept loaded down by one round so that in the event I have to select-load a slug all that is required is to feed the slug into the tube and rack the action. If an ammo change isn't required then it's easy enough to top off the tube from the side saddle. Right now I keep two buck and two slugs on the saddle.