I am obsessed with not giving my children GMO's at all. We live in the city and just planted a 900 sq foot corn field in our front yard!!! (I called the city to make sure it was okay. I don't think my neighbors are happy about it, but probably chalking it up to me being the "crazy chicken lady" and secretly hoping the Army makes us PSC!) I only feed my chickens organic feed, but who knows if they are lying about what goes into it, almost all the corn in the US in genetically modified.
You got good comments on raising broilers. Don't get attached, they grow fast, and more space the better. As for your corn batch, consider trying your hand at a diversified lot of various leafy greens and companion planting to best utilize a city lot. 900sq feet of mono culture on a high nitrogen demanding crop is a good start, but higher risk. Don't know your area, but leafy greens often give a better yield to space used and are better for you than corn.