I don't know if any country has the industrial base to do it yourself, as you say, but if any does, it's almost certainly China just due to manufacturing output and expertise alone. They're, what, 30-35% of the world's output? Set aside 30% of that and they can still feed a lot of exports to other countries - more than anyone else - to bring in money. And nobody else has anything close to the leading-edge hands-on know-how to build all the stuff that would be required. As you mention, there's a lot nobody has yet. So the country best at building cutting-edge hardware is gonna have the head start.
If you're a western pessimist, that whole mega-project could easily unlock even more manufacturing, materials science, etc, progress that could be applied to the rest of their output too, furthering the gap between them and everyone else. (But I guess if they did single-handedly save however many billion people from displacement, and the majority of developed countries from massive crisis/invasion/etc, that's probably the least of our worries!)