Here are a few things to consider to start:
First and foremost, geese are large birds. They require significantly more living space than chickens, and while they can eat some of the feeds provided to chickens, you have to watch the protein levels. Too much protein may cause the geese to develop "twisted wings" where the wing feathers stick out at odd angles (the same phenomenon is seen in ducks).
As a large member of the waterfowl family, geese shouldn't be housed with chickens in the same enclosure/pen. Geese can get sloppy with their water and turn things pretty muddy, and that makes it really difficult to keep chickens happy and healthy. I recommend giving geese ample water to swim in, even if it's just a kiddy pool, in order for them to keep cleaner and happier.
Additionally, keep in mind that unless you're buying goslings, adult geese may take a long, long time to tame down. The goslings I used to take to the fair were the only ones in the entire flock (12-15 birds total) that tolerated people exceptionally well. The rest of the flock would move to the opposite end of the pen away from me.
Most geese are not overly aggressive toward people, but they can become aggressive when the goose (hen) is laying or on the nest. Broody chicken hens may pick a little at you, but a goose's powerful wings can deliver a nasty hit. I have never been bitten or attacked by a goose (10+ years of poultry experience speaking here), but it's important to be mindful of the damage that can be done if you're not watchful.
Geese can be rewarding birds to keep, but they can be challenging for a beginner with limited goose experience. Be sure to do your research!