There is a very popular book called Five Acres and Independence that lays out how to do it on 5 acres. It's a bit dated though.

So, 5 acres is a good start. If you are going to burn wood, you need to build a coppicing woodlot and you'll probably need another 5 acres minimum to do that depending on latitude and other factors.

You might want to study up on permaculture. Under the permaculture concept you could easily have a self sustaining farm producing food and fuel for a family on 10 acres.

Beyond that, you might want a security buffer that keeps your buildings hidden from the main road. That would depend on the area, terrain, etc. which makes this entire exercise a bit subjective and dependent on local variables. 10 acres in Kansas is not going to be enough to hide a building, but 10 acres in the Appalachian backwoods is virtually invisible to all but satellites.

I have 15 acre place in the Kentucky hill country with 5 acres cleared and the rest is hardwood forest with lots of available water from two springs and a creek. You wouldn't know it was there if you drove by. I have a large garden and a few animals and I'm slowly ramping up to mini-farm status as the prices at the grocery store continue to rise. I try to use permaculture principles in everything I do out there so I don't have to buy any fertilizer or pesticides and the place sustains itself. I've also started coppicing a small part of my forest so that I only need to use a small area and can leave most of the forested land undisturbed.

One note I'll add... it takes years to develop a sustainable mini-farm. It's also incredibly hard work.