A truly sustainable home would be one that is constructed from renewable materials that do not damage the environment and that operates with little or no impact on the environment. It would be in or near a town/city to minimise travel and would manage rain and waste water to reduce impact on sewers, etc.
The maintenance of your sustainable home will generally be little different to any other home so keep gutters/drains/gullies clear, prevent piles of leaves/earth from building up against your walls, etc.
Fundamentally, more insulation is better than less. The more you can afford to use, the less heating will be required and the more sustainable your house will be, with a few caveats such as good airtightness, etc.
Thermal bridges are relatively easy to design out but it generally involves using systems and techniques which are inherently thermal bridge free in the first place.
This is a very personal question for most people as the desirability of a location is affected by popularity, access to facilities and road networks, cost of land, views from the plot, etc.