Decoys aren't necessary, but help. I use them, but I killed a ton of turkeys long before I ever had them.
Any full choked shotgun will work..12 or 20 gauge. If it has screw in chokes, even better, as you can get a turkey choke.
Lots of folks liking the new Winchester Longbeard XR loads made specifically for turkeys.
Whatever gun you get or already own, make sure you check that the point of aim and point of impact are one in the same with the ammo you are going to use hunting. If they are not, I recommend installing some rifle sights so you can adjust.
Bowhunting.....darn difficult to come to full draw without getting spotted with a group of turkeys on top of you. If you already have a ground blind, all the more fun.
Main thing... Keep it simple and have fun...turkeys aren't brain surgeons.
Good luck and good hunting.