Most immediate payoff will be annual veg, so plant those with a few perennial veg thrown in (asparagus, artichoke, rhubarb, chayote, etc.) to get started. Focus on substantial things like winter squash but also stuff you cook with. If you are comfortable growing tubers and legumes, go for it, but just start with stuff you know how to grow and don't get fancy. Preserve excess if you have it by fermenting which is super easy. Each year add more varieties and more perennials. Add herbs and spices and alliums.
Another quick and nutritionally beneficial payoff can come from learning to harvest a few local wild foods: berries, edible herbaceous and flowering plants, etc. like dandelion, oxalis, blackberry, persimmon, salvia, prickly pear, yucca blossom, whatever grows where you are. If this includes nuts, big win on the fat and/or staple food front depending on type. Consider making flour from wild nuts/seeds. Labor intensive but big calories compared to most wild foods which tend to be more supplemental highly nutritious but insubstantial (salad greens, berries). I use acorns, pecans, bloodweed seeds, mesquite, etc. Acorns abundant most places and can (at least partially) replace conventional flours for baking, breading, etc if you experiment a little with ratios. Also wild nut/seed flour can be used on its own to make flatbread. Nuts store long time especially if frozen.
Plant your fruit and nut
trees and berry bushes as soon as good planting time rolls around for your area. These are for the long term but a few may produce a little within a couple years. Learning to can jams and preserves not a bad idea and water bath canning quite easy. Many wild berries and fruits make especially good preserves, syrups, etc. so practice on those until your own fruits mature. Plant trees every year until no more will fit.
Chickens I think are great. Lovely easy eggs with no butchering necessary so not as much struggle or learning curve. Feed them scraps and forage, in small space probably need supplemental feed. Can glean fruit droppings as trees come into production. Mulberries, persimmons, other messy trees especially. Black soldier flies very good supplemental feed. Also consider growing extra for chickens in garden, but worry about this more as you get settled in unless feed costs are major obstacle. Rabbits will be all the meat you ever need and start up is quick, can forage much food for them but must butcher. Eggs very reliable, good fat and proein, very easy so my favorite. Get chicks in spring, maybe second year if overwhelmed with planting first year, or if you have a bit of extra money adult hens or point of lay pullets so you do not have to worry about brooding chicks or wait extra year for them to lay. You can have eggs and/or rabbits within a year or two easily.
Then learn to grow staple crops that store well. Dried legumes, tubers, winter squash, maybe grains. Also store nuts as mentioned above. This will help provide sheer calories and along with preservation by fermenting and canning will round out your lean seasons and years. You could start with these if you want most caloric bang for buck early on but I find people tend to be most successful starting with "normal" familiar annual veg and leaving grains, etc. till later.
Hunting or fishing can be a big win.
Aquaculture or raising insects also options. Consider learning to make some jerky or sausage or can meats.
Consider adding layers such as vining fruits and
mushrooms once systems are established and you have the time/energy.
Finally consider deficiencies--do you lack fats? Iodine, B12? Purchasing lots of animal feed that you could grow instead? Want to make your own teas or alcoholic beverages? Is there a lean season that you could address by planting something that ripens then? Do you need sweets--honeybees, maple syrup, sugarcane? Do you end up eating at the local Mexican restaurant while your squash rot on the vine because you are bored or worn out or out of new ideas for how to cook or preserve them? And so on.
I would say at a rough guess you could get to producing 75% of your own calories within 3 to 5 years. But you probably won't because you'll find it unexciting, laborious, and fraught with unfamiliar foodstuffs. This is what I have observed and to some degree experienced. Depends a lot on the person and climate.
Theoretically it is possible to do with much less space but my gut and experience says that less than an acre per person is marginal. Depends a lot on climate again and what you like to eat, and if you have access to additional land for wild harvesting or like minded neighbors to trade with for increased variety. Could probably live with much less land if willing to eat mostly grains/legumes but who wants to? One acre gives room for less intensive but more interesting and diverse plantings (like forest gardens) and some room to play around.
Finding people who already know how to do what you want to do saves much time and shortens learning curve on things like
beekeeping, wild harvesting edibles,
food preservation etc.