The first step is not to wait for that farm. Urban homesteading is a way of life for many of us. Begin by learning skills that you would need if you ever do find that perfect farm.
Sustaining your self begins with food. Try buying your foods in season from local farmers markets. Learn to can and preserve those foods to last you throughout the year. I can everything from your basic vegetables to making my own soups, catchup, spaghetti, bbq, picante and other sauces. Buying locally grown produce in season is VERY cost effective and helps your local farm economy.
Next while at those same markets ask around about locally grown meats. I got several friends at work together and we regularly buy a grass fed beef. The farmer hauls it to the butcher shop for us and we pick up frozen wrapped meat for about $2.99 a pound. This is everything from hamburger to inch thick T bones! Buying meat bulk in this way keeps me in WONDERFUL meat for about a year. My family also buys 1/2 a pig, and two sheep this way each year.
Herbs are a good way to start gardening in a small space. With a good dehydrator (MUST HAVE -well worth the money)
you can raise fresh herbs enough for your family and evento sell in a few flowerpots. I also dehydrate onions (purchased from the shriners), mushrooms and celery (on sale at the grocery store), and (fruit from a local u pick ).
I live in a SMALL yard (40x120). I raise as part of a very decorative landscape: grapes (enough to eat fresh, freeze, and make jelly), Peaches (my dwarf tree produced 60 pounds of peaches last year!). I also have bush cherries for jam and a grafted dwarf tree that can produce apricots, plumbs, nectarines and peaches on the same tree. There are also apple and cherry trees available that produce several different kinds.
I have a small garden plot. I grow tomatoes, peppers, climbing beans and I have two half barrels (recycled Pepsi syrup containers) that I grow salad in.
In my area chickens are legal. I keep three hens in my backyard as pets. They provide all of the fresh eggs my family of three can eat and part of the year I have eggs enough to give away. Broilers are also relatively easy to raise I lease a space at a friends farm to raise my own chickens to eat each year. I can raise enough chickens for my family to eat as well as the person who leases me the farm spot's family. It takes less than 4 months from start to freezer to raise broilers.
I make my own soap and laundry detergent, I compost my grass clippings for the garden (with the litter from my hens it is nice indeed!), I drive paid off older vehicles, I buy clothing on sale or recycled (thrift stores). This is how I urban homestead and I am not alone!
Some day I hope to own a small farm - until then I learn!