In some German villages you can buy old self-sufficient properties. Those were used after the war for families to sustain themselves from what they grew. You see these in sizes from about 1000 to 3000 m² – 10700 to 32200 ft².

Granted, those were used to feed a large-ish family with 1950s tech and no synthetic fertilizers. Still, it goes to show just got much space you need if you want to be truly self-reliant. 200 ft² is very small and probably makes you heavily dependent on things like commercial fertilizer.