Wow your questions cover what take a lifetime to learn. How do you want to hunt geese, how bad do you want to eat goose? If you skybust you want bb and bigger, if you decoy close you can start with 2's and end with bb for the "up yours" shot.
Patterns have to be checked but generally you want the most steel in the air your chambering will allow.
Loading starts with what press you have, if you have none get one that will accommodate steel readily. Steel is troublesome but shot gun loading is less finicky in general than rifle, but still will not suffer foolish shortcuts being taken.
You need a good book, like "status of steel" from Ballistic Products. and a mentor would really help on that wild adventure we call goose hunting.
