I once read that you need less than 600 square feet per person to survive. Personally, I want more than survival.
What do you want?
If you eat three eggs each for breakfast, and use some for other purposes, you will want a dozen or maybe more eggs per day. You need as many hens, along with a rooster. We (there are three in my house, but one doesn’t count) eat less than a dozen eggs per week, most weeks, so three hens are enough for us. Excess eggs can go into the incubator, and the chicks can be sold if they are not needed for meat. If you don’t want to use an incubator, boil the eggs, mash them, and feed them back to the chickens, or save them for the pig, dogs, and cats. To feed the chicks, plan on letting them run part of the day, if you can. Plant desirable food plants too, whether you plan to grow your own feed or not, the fresh food is good for them. I have read, though we never did it, that one large zucchini and 3 lbs. worms per day is all you need to feed a dozen chickens. Chicken feed and soil amendments from a minimum of space, effort, and expense. Or give them 4 oz grain per bird daily.
For milk, do think about getting goats rather than a cow. One milk goat will produce all the milk you can use while she is lactating. Two, bred to alternating schedules, should leave you with excess all year around. You will need less than 1/2 acre of decent pasture for them and the chickens together.
If you want beef, you should need no more than one calf per year, and I would suggest that you find a dairy in the area, and buy from them one male calf each year. Have a goat coming fresh at the same time, and raise the calf on the goats milk. You will have some of the healthiest calves in the area. Plan on butchering them young, as they take a lot of space as they grow up. Castrate if you are letting the calves grow much over a year, or they will want to visit the neighbour’s cows. Raise them in a pen for three to six months, and feed them only milk for excellent milk veal, or let them eat grass and raise them up to a year for good, lean beef that is still technically veal. This should be plenty of beef for a year, and won’t take over 1/2 acre.
If you really want cow milk, look into Dexter cattle. They are a small breed of multi-purpose cattle. Two cows can run on two acres of good grass, and give you all the milk and meat you need, with some left over. You will most likely need to feed them, though.
Think carefully before getting a milk breed of cow. She will produce five or more gallons of milk per day for 305 days per year. Many cows can give over 13 gallons per day. She will need lots of grain to do it, and you will need time to milk her, twice every day. Even the dexter will give a gallon per day, which is a lot for three people. Don’t forget to make butter and cheese !
Pork is good. You can often pick up a weaned piglet for under $20, sometimes under $5. Feed it those leftover kitchen scraps, milk, eggs, and let it clean up the garden every year. Butcher at less than 100 pounds, and get another for the next year. Or go to the pork auction and pick up an old boar for less than 5 cents per pound. Take him straight to the butcher though, as he is strong enough to tear up your barn, and will, just for fun. Don’t even think about breeding your own hog.
One acre of orchard should do for you: 4 Cherries, 2 apples and 2 pears around 30 ft. apart, 2 Peaches at 20 ft, 2 plums at 15. I’d add 100 strawberries, 6 blackberries, 6 raspberries, and 4 grapes to the mix, as they will bear sooner. A few nut trees would be good to add, if you can grow them where you are. Maybe 2 pecan (35 ft), 4 hazel (15 ft), and 2 chestnuts (30 ft). Even if you put in a 50 ft row of asparagus, 4 hardy kiwis on a trellis, and 12 rhubarb plants, this is less than an acre. Fewer trees if your neighbours have them close enough for pollination, and closer together if you get dwarfs.
I don’t know what you are gardening now, but 1/2 acre is a lot of garden. 330×66 ft, re-arranged in whatever shape it comes in. I wish my spell-checker worked, that word looks wrong. Point is, there should be plenty of vegetable and herb gardens.
Add at least 1 acre if you need a woodlot, and 2 or 3 for growing your own grain, though I don’t recommend it. Add 2 beehives to the orchard, if you can, and spend all you can on GOOD fences.
Five to ten acres should be enough for three people, if you get decent land, put up good fences to keep out the vermin (deer, coyotes, feral dogs…), and put in the work. More would be nice, though.