pretty much any gun works but is it best that you pick up something modern with choke tubes so you can adjust for conditions if needed. If your not sure you will stick with it you can easily pick up a used 500 or 870 under $200 and not be out much if you decide not to follow thru.
Do not worry about all the "fancy" shot out there either. Everyday steel shot works great (I have tested it all in the past 30+ years) and at decoy range and even out farther you will have no problem killing ducks and geese with steel.
a good set of Waders is a must (an hip boots for warm days) neoprene over rubber and a rainproof jacket.
also you do not have to spend $100+ to get a good duck call
welcome to the Addiction