1. Definately 12 if those are going to be your main quarry (sp?)
2. Definately a semi-auto (or auto-loader) because turkey loads are pretty stout and duck loads aren't bad either.

The 870 is a fine gun, but I really don't see the point of getting a pump for a gun to be used with heavy loads! They're argueble the worst when it comes to recoil. Do your parents know much about guns? Just tell you you'd like a 12guage auto. If not, visit here: http://www.shotgunworld.com/new.html Don't be scared of the cheaper guns from huglu/spartan/charles daily/verona etc. Often their designs are EXACT copies of the more expensive ones...and make fine guns. You can also read for weeks at that forum and learn more about shotguns than any one person deserves to know without decades of trail-and-error.