And in space you don't need oxygen?

Yeah, that is a weakness of the plot, the station they built at the end with the gravity tech would be susceptible to the blight too I assume (if all it's oxygen comes from vegetation).

Vegetation will have to be on the station either way - people need to eat something.

Again, the point is that if you build some self-sustained habitat structure in space, there is zero reasons, why you can't build it on Earth.

Yeah, it would of been better if the crisis affecting Earth was more destructive, like a Solar flare coming to destroy everything, then the idea of finding a new world in another galaxy would make more sense.

Well. if the same happened to Earth what happened to Mars a long time ago (ie. the core finally stopped moving, the planet lost its protective magnetic field and hence the atmosphere just kinda slowly evaporated to the open space), we'd need to build some kind of physical protective layer around the whole planet to stop that from happening (and stop the cosmic rays that tear the atmosphere away). It wouldn't be fun at all seeing the atmosphere and seas slowly evaporate to open space... heck maybe it is already happening but we are not just paying attention as it is such a slow process at the moment, thanks to the protective magnetic field.

In such a case, it might be more feasible to build some kind of smaller scale space station, than trying to cover the whole planet with some new protective layer.

And we can't just build a dome the size of space station on Earth, because?