Vines and roots seem easiest to me. Vines = tomatoes, cucumbers, squash (including zucchini and pumpkins too), etc., etc. Plant when warm weather is coming, use a lot more fertilizer, and let them spread, get huge and give you a ton of fruits. Easy peasy. By roots I mean roots, bulbs, tubers, etc. Nearly all are easy, except carrots are hard to germinate. If you've grown carrots and lettuce I think you're already a step ahead on difficulty and shouldn't have that much trouble with any veggie.
If you're getting a farm farm and not just a little plot of land then you might need farmer advice rather than gardener advice. There's machines, large scale irrigation, etc., etc. that I can't answer. Could also change which plants are easier.