Concerning the ideal psychological makeup of a crew, I think long term the answer is scaling everything up to incorporate more and more people. Safety in numbers, and strength in diversity. Consider just that one question about whether to send single people or married couples- if you send only a small number of people, either choice you make has it's limitations. Married couples can divorce, and be forced to live in close proximity to each other. Single people only have so many options, and there's no realistic way to match people perfectly while simultaneously giving people freedom to make choices, which we basically need for it's own sake. Only one way around it, we have to build cities in space: some with dedicated orbits around celestial bodies, some mobile.