As far sustainability goes i think the countries we should use as examples would imo have to be Iceland, Norway, Greenland, Netherlands and etc.
Iceland and Greenland for been progressive in the renewables area, Norway for how quickly they've been adopting electric cars and their cities seem to be pleasant and look quite nice from what i have seen? and Netherlands for their focus on cycling networks.
If we could combine the thinking of these countries and figure ways for it to work in larger countries we'd be well on the way to making a brighter future, hell, even if we just got the rest of the world having the same attitudes towards electric cars and renewable energy as Iceland Norway and etc do we'd be making pretty big leeways.
Of course the one biggest issue that isn't so easy to solve is actually not having so much waste in the world and decreasing how much we consume and move to consuming it in a more sustainable way.
Probably one of the biggest issues is how unsustainable our use is for paper which means deforestation on large scales, if we could get the paper milling industries and plantation companies to use hemp paper that would help a lot since it's easier to grow and doesn't need quite as much space as normal trees and this would also mean there'd be more wood for crafts for things like furniture and etc.
