First of all, welcome to the T&TH forum. We're glad you're here and look forward to hearing more from you. This is a good place with helpful folks. Everyone has "favorites" or something that has worked for them, so you should get lots of good information. The good news is that there are many excellent choices.
Turkey hunting need not be a complicated sport. The main thing is to go out and enjoy your experience in the woods. Like any other sport, it's one that's learned over time spent in the woods and to some extent at the range, learning about your equipment and how it works for you.
Guns and turkey chokes are a couple of the favorite subjects here, closely followed by what shells go in those guns and through those turkey chokes.
It's hard to beat either a Remington 870 or a Mossberg 500 shotgun. Both are well made guns, have many options available for them and are very reasonably priced. The Benelli Nova and the Mossberg 835 are also excellent guns and if you found one that had a better price than the 870 or 500, it would be a good choice.
While there are those who really like single shot, single barreled guns, as I do, they would not be my first choice for a turkey gun. A second shot is sometimes necessary and it's good to have that option.
I'd try to shoulder as many of those guns as possible and see how they feel to you. The choice of a gun is a pretty personal thing and sometimes one of those guns will just feel better to you than another one.
I would suggest that you choose a gun with a 26" or longer barrel. It's just easier to get a gun with a barrel at least that long to get good patterns. That's not to say that a shorter barreled gun won't get good patterns or kill a turkey, it's just more of a challenge.
Some basics, after you've found your gun are a good "deep cleaning" of the barrel http://www.allaboutshooting.com "Cleaning a Shotgun Barrel"
and then clean the fire control unit (trigger group) since we're shooting a shotgun more like a rifle, you need a clean, crisp trigger pull.
A good after market turkey choke will help more than can be imagined, if you've not shot one. There are several good brands and a wide choice of exit diameters with those chokes. Exit diameter is really of less importance, in my experience, than the internal geometry of the choke.
I try to shoot them all and have found that it's largely a matter of how much you want to spend. I have excellent results with and often recommend the SSX line of chokes. They are truly a premium quality choke with a very moderate price tag.
Shotshells vary widely in price and most turkey loads are either lead alloy or tungsten-based shot, like Hevi-Shot. My top choice in lead is the 3" Winchester High Velocity (HV) shell with 1.75 oz. of #6 shot. It's reasonably priced and has probably accounted for more dead turkeys than any other shell. My top choice in tungsten-based shot is the 3" Hevi-13 "Bronze" shell with 2 oz. of #6 shot. Either will kill turkeys when we do our part.
Lastly, range time is just very important with your turkey gun. Since we shoot that shotgun like a rifle, you need to see if you gun has the same Point of Aim (POA) and Point of Impact (POI) at ranges from 20 to 40 yards generally. If not, you may need to add some sights. Open sights like those made by Truglo or Williams work well and can get you on target.
Shooting at some "big paper" at least 3' x 3' will tell the tale on POA/POI issues. Shooting from a rest and then shooting from a turkey hunting seated position are best in my experience.
Please come back and I know everyone here will be of help to you.