Really, if we can solving the issues required to solve for constructing facilities that can house the population, then we'll have no need to stress the Earth's ecosystem by imposing our needs upon it, and sensibly grow what we need where we don't have to fight gravity to get it to us. And eat it fresh. There's a lot more room in space, and we can top up the deficits in the global production levels which are almost assurdly to rise as time progresses, and as our production capacities increase our requirements to trade with Earth will lessen to the point where they have nothing left to productively give and we have more than we can even waste. So it makes sense to just give it to them, and thusly end world hunger. By simply giving everyone food.

Might as well save the money on freeze-drying equipment. There's no chance of us building any serious facilities any time soon, so have no need for freeze-dried foods for "space" and by the time we can build such facilities, we'd of already started on the supply chains to ensure the Earth isn't required for our survival.

There's no hope of Alpha Centuri this century, and that's if we left now. It's quite some way away, will take a long time, even at light speed - which we can currently get nowhere near, theoretically something like the EM-Drive/Q-thruster could achieve 2/3rd light speed, in about 40yrs of accelleration.... That could get to Proxima Centuri(slightly closer) in about 85yrs or so, accounting for braking.

3D printers and "robotics" will indeed be useful, but we need more than that. A 3D printer can only do so much, other tools are required like milling machines - the debris from which in microgravity might become an issue.

Quanto aos detritos, podem ser lançados contra a estrela mais próxima por exemplo ;)

As for debris, they can be thrown at the nearest star for example ;)

Anything that can be used, should be. Don't burn it, harvest it.