I think this is mire a "proof of concept" rther than a pre-colonizing mission. Its all being privately crowd source funnded.
Selecting Alpha Centauri was just convenience to the first neighborhood exo-star.
If we were looking at pre colonization, I guess Hawking would hve chosen Barnards Star because it has several known earth sized planets (maybe some goldilocks ones)
But Barnards would take another 30 to 40 years back and forth.
Having proof of concept for sub light travel is just another barrier to break.
Itll be a neat trick to get this done and then we would worry about scaling UP.
Usually scaling up provides a logarithmic increase in energy and complexity not an arithmetic one. SO I think we have to be able to talk from some experience. Even the first moon shot was done in relative (albeit easier) baby steps .
When the sun dies, its gonna first begin burning Helium inan ascending energy budget. The inner planets (ll the way to Mars, will be engulfed in rather warm weather). That fact is what these guys are working from. Their work is just a first step in developing an intergalactic moving van