I don't think growing food would be a problem. Yes the sun is further away but it's still bright enough to grow food in a sufficiently modified botanical environment. If you can still harness the power of the sun, you can grow food for free, once the environment has been created. Once the startup water for this system has been installed, it can be recycled indefinitely, for both humans and plants. The beauty of water is that if it's kept inside a sealed environment, it never changes and can be filtered repeatedly. The biggest problems for humans would be physiological (managing illness and ageing) and psychological (living in a container for the duration of life; keeping motivated; living with regret and loss).