This is presently true. My point is that it's a conservative estimate to say we'll be capable of it within the next 1000 years. Our biggest issue currently is the high cost of getting payloads into LEO. For Apollo and the Space Shuttle that cost was ~$50,000/kg. Factoring in reusability it's now estimated to be $1000/kg or less. There are paths to get this much lower (eg <$10/kg).

Mercury has specific issues and advantages. The biggest advantages are access to energy, high orbital velocity and no atmosphere. A thin atmosphere like on Mars is the worst of both worlds. It really just makes landing difficult and creates dust storms to cover your equipment in dust.

The high orbital velocity of Mercury is both an advantage and a disadvantage. It makes it really difficult to get there, which is why there have been relatively few missions there, but once you are there, it means the delta-V of getting anywhere else in the Solar System is quite low, whether that be finished products or just raw materials.

Mercury is metal rich but probably lacks elements like oxygen for, say, smelting steel (and, of course, living). The long day/night cycle is an issue too.

My point in relating the mass requirement to Mercury is because, even though 1% of Mercury is still a lot of mass, it would still leave Mercury relatively intact. It's also metal-rich.

I had another vision, informed from science fiction. It was that we could send relatively small machines (self replicating using local materials on the asteroid) and they could do everything we want after we figure out the replicating w local materials part. And because we only need to send a small starter robot it doesn't use that much energy.

What do you think of that? I mean we could do the same with materials to process them on Mercury.