But you would also need a lot of cargo to support those people. In fact, your cargo to person ratio is going to be quite high. It would probably be 10 cargo trips for every human trip, so more like 100,000 trips. And we're talking 100,000 trips of a giant spaceship.
And what is the cost, both in terms of resources and pollution, of launching 100,000 times? Even if you kept it in orbit and brought people up to it it's a huge cost.
And I'm betting 100,000 launches is more than have been done in all of history. By a rather large amount, I'd think.
As usual, when I hear futurists telling us about the awesome the future will be ... I find myself thinking "this is impractical, way more than anybody will ever be able to afford, and probably never going to happen".
It sounds like we'd need to pretty much strip the Earth of resources to pull this off, and unless Musk is paying this out of his own damned pocket, I think the entire idea is doomed to fail. And that doesn't change the fact that you're diverting a huge amount of resources for a relatively small percentage of humanity.
This is flying cars, Mr Fusion, and a vast amount of engineering, plus ponies, unicorns, and cats living with dogs ... all in one big overly-optimistic ball of fantasy.
The sheer amount of energy required to do this is so mind boggling as to make the whole idea laughable.
I think the romantic idea of space colonization is pretty cool. But I don't really think it's quite as viable as people like to think it is. At least not with current energy requirements and sources.