Fences? Six feet, and free of ‘sharp corners.’
Their entire environment must be kept scrupulously clear of bits of wire, glass, screws, etc.
I am tame-wild emu guy. You should wait for folks who have pet emus to advise you on feed. My note is always: provide any greenery you can in their paddock: grass, other edible plants, fruit trees, etc. – particularly anything that will grow during dry times. Emus love ‘fresh pick.’
Costs? Over the years, we have noted that veterinary costs, both for shots/check-ups and emergencies, can be a real difficulty. Apparently Giant Flight Bird Vets are few and far between.
Space? Lots of space. As much as possible. BIG space. (And they love to swim).
And overall? Emooz are a big investment. They are lovely people, and apparently can live in harmony with other critters on hobby farms.
But they are big; best kept in a pair or more; and live around fifteen years. People buy a cutie cutie chick, and two years later it is literally big enough to bust through fences.
So, if you really want emus, then get some. But if it is any sort of spur of the moment thing, I counsel more research.
Supreme Emu, Lake Muir, Western Australia
[A mob here for breakfast. Mr. and Mrs. Bird. The two sooky females. And OO7 and her posse.]