The one (and only) thing geese will guard against, or at least warn other birds about, is birds of prey. I don't think most types of raptors are going to attack geese unless they're especially small, so I think you'd be fine with medium sized geese.
Other predators will easily kill geese. In...
If you just want a few geese to keep as pets, I suggest getting smaller breeds because they'll require less feed.
If you think you might hatch some out, maybe consider a more rare breed than Embden or Toulouse and keep all of one kind so they breed true.
How many you should get depends on your...