IMO the first accessory that should be installed on a HD shotgun is a good white light, and my personal preference for one of these is one of the SureFire fore ends. Others here have rigged lights on rails and seem to be happy with them also. For me, using a light with a pump shotgun just works much better with the dedicated fore end, but the price is a bit high if you have several guns to outfit, or are on a tight budget.
Ghost rings...properly installed...are good sights, but there is nothing at all wrong with a big, bright bead for practical uses, nor for getting into something like 3 Gun. (although, if you get serious about that, you will probably decide to get an auto and jazz it up some).
If you get a light installed, be certain to take the lamp and batteries out before long shooting sessions at the range, as repeated, heavy recoil can eventually kill even the SureFire set up. No need to break parts trying to prove a point...they work fine for real world situations.
Try Grant at G&R Tactical, and / or Calvin at Brightflashlights for lights and related parts...both are good guys and both support this board as registered dealers. You can find their info in the Industry Forums.