A far smaller gravity well.
The amount of resources in a single asteroid are far greater than would be needed. There's more steel in a 1 mile wide iron/nickle asteroid than has been used by humans in our entire history to date.
If you really want to talk about a resource rich environment, then I suggest building space colonies in orbit around Saturn, Neptune, and Uranus. Not only do you have resource rich moons and rings, but strong magnetic fields that can be used for radiation protection and power generation.