Domestic geese cannot fly, so you don't have to clip their wings or worry about them flying off. Ganders can get aggressive during the breeding season, so be aware of that. My geese have never acted aggressive towards me. You probably don't have to worry about your geese attacking you, aside from maybe an aggressive gander during the breeding season.
Their care isn't too different from ducks, but they are primarily grass eaters, meaning they need to have access to grazing. They will eat mostly grass when it's available, as well as munch on whatever feed you provide when they want to.
Also, it's been mentioned, but geese won't really 'guard' or 'protect' other birds, in the sense that they're not going to try to engage or fight off a predator. Their size may deter a smaller predator from trying an attack, but all they'll really do is alert loudly at the sight of a predator. So if you're around you'll know something is wrong and can go outside and investigate, but if you're not around and a predator decides to attack, it's probably still going to get a bird.