This type post will generate opinions from one extreme to the other and thats a good thing! I'll give you my opinion along with everyone else and you can sort through them and really get confused.
Pump guns are probably most practical and are generally very reliable. Twelve gague rules simply cause it throws out more shot. Interchangable chokes are desired cause you will most likely want an after market choke either now or later. A 3 in chamber is adequate unless you enjoy having a sore shoulder.
A turkey gun takes a beating in the field and some are a lot heavier than others cause they are all steel(such as the Rem 870 Express which also kicks like a mule). I don't like anything plastic on any gun cause sooner or later it might break.
A sling is a handy thing to have also along with some means of attaching some sort of sight system. A must have for turkey hunting.
Yes, you will want a sight either a turkey scope or my favorite a standard peep sight.( if you get the peeps find the all metal ones that are fully screw adjustable)
Confusing right? Good Luck with your selection.:banana::banana::banana: