I agree that the Remington 870 is a good beginner's gun. Look at the different finish levels and decide for yourself how much you want to spend. The cheapest ones are the plain jane Express models which have the cheapest wood and and a matte finish, (which may be what you want for a turkey gun). I've always like the Wingmaster, with the traditional blued finish and walnut stock, but I grew up duck hunting.
Get a 12 gauge. A 20 gauge does not necessarily have a lighter kick. Lighter guns have more recoil. If the 12 gauge kicks too much use a lighter load. I shoot 1000's of shells a year from a Browning over/under 12 gauge. It is a nine pound gun. I have no problem with recoil even with heavy target loads. Shooting the typical 20 gauge target load with the kids' 870 youth model just tears me up. It's just too light of a gun for heavy loads. We do have a 20 gauge Beretta AL391 that's a dream to shoot though. The gas operated action really soaks up the recoil.
Get a 12 gauge. A 20 gauge does not necessarily have a lighter kick. Lighter guns have more recoil. If the 12 gauge kicks too much use a lighter load. I shoot 1000's of shells a year from a Browning over/under 12 gauge. It is a nine pound gun. I have no problem with recoil even with heavy target loads. Shooting the typical 20 gauge target load with the kids' 870 youth model just tears me up. It's just too light of a gun for heavy loads. We do have a 20 gauge Beretta AL391 that's a dream to shoot though. The gas operated action really soaks up the recoil.