We would need a lot of people on the mission for genetic diversity but you couldn't exactly have a hook up culture. We would need a type of multi generational arranged marriage/arranged sexual partners based on genetics. Then what happens when the heart wants what the heart wants? I would have hard time seeing this not turn into Lord of the Flies in Space even if the engineering parts were solved.

> to build stable closed ecosystems

Sealed terrariums? Unless you mean something more complex than plants, soil, sunlight, and water?

https://laidbackgardener.blog/2019/10/14/the-worlds-second-o...

"That means it has been growing inside its bottle with no additional air, water or fertilizer for 47 years."

... and once you get to the destination you have to build your whole industrial infrastructure from a tiny seed.

It's bad enough to do on Mars (or an asteroid or other solar system environment) where you can get spare parts sent over in a few years and ask ground control for answers to problems, have them simulate things on Earth or in cislunar space and put a lot of engineers on it. The more I think about it the worse it seems in our solar system -- but interstellar travelers are truly on their own.