It's best to start small and expand with the years and experience. For example, one tomato plant per person is really sufficient, unless you plan to be the supplier of your neighborhood or want to sell them at the Saturday Farmer's Market. Vegetables must have good, loamy, well-drained soil. Most backyard soil is not perfect and needs a helping hand. Check with your local nursery or county extension office about soil testing, soil types, and soil enrichments.
Placement is everything.
Like humans, vegetables need proper nutrition. A vegetable garden too near a tree will lose its nutrients to the tree's greedy root system. On the other hand, a garden close to the house will help discourage rabbits, raccoons, deer, mice, and opossums from nibbling away your potential harvest. Vegetables need lots of water. At least one inch of water a week.