CerberusGate
I should save my game in a whole new slot
It's difficult. If one were to take the structure spoken off in mind, it would mean that the town would lie inside a crater and that there would be a lot of metal structures around. Plus since 4 had an entire stadium turned into a town, one could reasonably assume is what they see of 3's Megaton is representative of the actual town: a lot of buildings in a deep cavern with little room for additional essentials like crops and animals.I don't honestly get the "no crops" thing or "no animals." Because the structure isn't literal. Megaton is a representation of the actual city.
Game engine limitations prevent it from actually being the size and shape it would be in a "real" setting.
You just have to assume the crops are there.
Plus New Vegas managed to do it in the starting town alone. Even 4 tried to do it at the expense of everything else (since there were very few set settlements brimming with content).