If you are setting up for HD and buckshot is your primary ammo, then a bead sight is plenty. I agree that you may want to look into a good weapon light. Surfire 6P with an LED head has been recommended to me by many folks. Mounting may take some creativity. I would want it mounted on the forend but I personally don't want to buy a forend that is fully railed, just to be able to put a light on it. I'm thinking of doing some modifying with a dremel, some epoxy and screws to mount a rail section to a standard forend on my 870. I've had a Mossberg 500 for over 20 years that has been a great shotgun. The Maverick seem very similar, except for the location of the safety. I kept mine simple and really the only mods to it were adding an ammo carrier and sling.
You may want to look into a way of keeping ammo with the gun. Since shotguns face the challenge of holding a pretty limited ammount of ammo, and grabbing it in an emergency, you are basically taking the gun with only the ammo onboard. I have a side saddle on my Mossberg and think it is one of the better methods for keeping rounds with the gun.
Also get out and pattern that thing with a few brands of Buckshot. I've seen dramatic differences in pattern size between standard loads, reduced recoil and reduced pellet loads and Federal's flight control loads. Always good to know what the limitations are for keeping your pellets on the target.
Good luck on the project.