First of all, welcome to the T&TH forum. It's a great place with lots of folks who will try to be of help.
The 870 is a great choice. Those are fine shotguns that will last a lifetime (or more) with reasonable care.
I would recommend that before you shoot it or pattern it, you "deep clean" the barrel. While it may look clean, it probably still has some residue from the manufacturing process and perhaps some oil or other contaminants. I'd recommend http://allaboutshooting.com/article_info.php?articles_id=242
As far as chokes go, a good bit depends on barrel length and shotshell choice. It's hard to go wrong with 3" Winchester HV (Black Shells) with 1.75 oz. of #6 shot or if you want to shoot tungsten-based shot, the 3" Winchester Xtended Range Hi-Density Shell with 1.75 oz. of #6 shot is a great choice. Both of those shells are very consistent performers and will deliver excellent dense patterns at 40+ yards and have enough retained energy to cleanly kill turkeys.
I recommend the SSX Turkey Choke. http://allaboutshooting.com/product_info.php?cPath=23&products_id=74
It's rated for all lead and tungsten-based shot, has great internal geometry and is very reasonably priced for a premium quality turkey choke.
That choke with either of those shells and your new 870 should be all that you need to take a nice bird in the turkey woods this spring.