#1 welcome to MO!
#2 do you own a german pointer?
#3 if you want advice from experts whyh did you come here?
just kidin, just kiddin...
So the firearm would be the 500 Persuader 20" with a matte finish which does exist! However, due to OFMs new site layout I don't know how to find it, but I believe its listed as a special purpose model.
The stock may be found on amazon for a decent price, I recently discovering that I like the ATI Talon stock though it isn't designed as a recoil reducing stock thought the grip and recoil pad are designed to absorb much of the energy transfer of the recoil. There may even be someone on here with a Knoxx stock for sale, you can check our classified section. Possibly Ebay too.
My personal feelings regarding pistol grip stocks on Mossbergs is that I don't prefer them only due to placement of the safety and action release, though there are a number of folks here who use them and say with a little practice manipulation of the mechanics can easily be accomplished. Because of my preference I use a Hogue short length of pull and the reduction of felt recoil comes from standing square behind the gun.
The forend with the light can be the most expensive part. Your options there include the Surefire or EOTech Insight. It would almost certainly cost less to purchase a mount like the Laserlyte trirail or CDM Gear BMT or similar mounts and then go with something like a Streamlight Polytac or TLR for example. There are many others out there. I use a CDM Gear clamp with a 3 slot rail and mounted a Coast Products TX40 with momentary on tailcap switch as far forward as I could get it on my 590A1 and then switched the tail cap to a remote tape switch ran to my forend. The reason for havin the light as far forward as possible is to reduce shadows cast by the muzzle, the distance from the forend also necessitates the need for the remote switch to activate it.
When using a light (or simply considering one) keep in mind the light isn't for navigating in the dark or in low light. Its to be able to ID what you may intend to shoot. Whether or not the bump in the night is a friend or foe, a loved one or threat.
I think a bead sight is fine for HD, but can be difficult to point at a target in low light or no light. For me, this meant gettin a tritium night sight. There are a number of these available, but I went with Meprolight. This is another topic we have a decent bit of info on already and should come up in a quick search of the site with the search feature at the top right corner of the page.
Don't forget to take your choice of ammo into consideration for your HD plan, practice aand see what needs to be changed first, but chances are, switching the stock to a more comfortable length of pull for both you and your wife will make a noticable difference in feel and ease of use as the factory LOP is rediculous at 14" +. One of guys had suggested that the factory LOP may have been designed around pro NBA players...
The least expensive way to do it may be to do one piece at a time, or to search and shop around for the best deals and get combined shipping. Watch for sales commin up for the holiday shoppin season. You may find coupon codes for %'s off and or for free shipping. There are a lot of places and choices to purchase from.
#1 piece of advice, practice practice practice. Gadgetry will never equal competency, nor will it be a surogate for practice. Know your firearm like you know the curves of ... uh, your hand.