First, I typically use BB for geese. I like Fastseel by Kent. I use steel all the time because $5 shells seem hard to justify for any hunting! I know that some of the "heavy" loads are great, but they need to bring the price down for me to use them regularly. Also, I usually use 3 inch shells. A lot of guys like 3 1/2 but with good shooting, 3 1/2 isn't needed.
As for decoys, buy quality deeks and build you spread with your hunting partners. I try to run a mix of mostly feeders for the fields and run around 10 to 1 feeders to uprights. Late season, I like to run sleeper shells. Also, it depends on the time of day. Morning= feeders, mid-day=sleepers...but, that is not a hard rule by any means!!! Just watch the geese for the time of day and try your best to set up the same as they do!
I recommend that you buy Goose Society, Goose Society II, and Lynch Mob the science of hanging 'em low volume two. These are great videos that really break down how to set up, where in the fields to set up, and also some good calling advice. I think you can learn more from those videos as a beginning goose hunter than by a few posts on this forum. By seeing what the pros are doing, you can take a lot of the trial and error out of it.
As for brands of decoys, that could start a real fight on this forum. GHG, Big foot, Hard Core are all good brands. Just as with everything else, each style of decoy has pros and cons and there really isn't a best decoy i.m.o. What counts is confidence in your spread! The next debate that could start a riot is shells or full bodies. Again, they both have pros and cons. Shells are cheaper and work great if you use them on motion stakes and balance them to match the heads. I wrote a post on it a while back that may be of some help explaining what I mean. They are cheaper to buy and you can carry more to the field.
Full bodies are more realistic and look awesome! But they are more expensive and harder to carry to a field... The newer fully flocked decoys have virtually no glare off of them, but hunters have used painted decoys for years with success. I highly recommend at least flocked heads because black paint glares more than you would think!
Whatever you buy, don't forget that slotted bags are a great way to protect your investment. Most of the paint gets chipped when they are in a bag, not sitting in a field!!!
Don't forget a good layout blind as hiding is probably the most critical aspect of field hunting. After you get a blind, dust it with flat tan or brown paint to knock the glare off and make a bucket of muddy water to spash on the blind. Buy one that is roomy enough for you and as low profile as you can find. Also, make sure it has stubble straps to add vegitation to it from where you are hunting.
Calls are something that everyone has an opinion on and they are all different. The best advice that I believe everyone would agree on is to go to a store that will let you blow their calls. Don't look for a brand, just blow every call you can. Think of it as picking out a new bow...One will fit you better than the others. Buy that call and learn to blow it well. Watch you tube videos, there is some really good stuff out there. Personally, I like Zink and Lynch mob, but there are so many good calls that it would be impossible to say what call is best and be able to back it up... Find what fits and don't get set on a brand until you see if it works for you...
As for what field type to hunt, geese are just like deer. They will eat what they need when it is ready, i.e. corn during cold snaps. Your best bet is scouting, scouting, and scouting... Scout during the time of day you plan to hunt...
I hope this helps you out some and I wish you the best of luck. This may not be the best advice, but trust me on the videos!!! They will teach you more than I can in a hundred posts!!!! Good luck!