I could put up one friggin' big Space Hotel, for starters. The kind that spins.

Still working on the details of giving everyone both gravity AND a nice view of the Earth without making them sick watching the Earth spin around.

And what's wrong with launching solar power panels?

What I think would be a good first use is an unmanned tour of the Solar System with a destroyer-sized space probe. Orbit the various planets for a few months, then buzz on to the next one. Thousands of scientists can put their favorite experiments on board.

Then, we do it with people. Shorter trip, though.

(Haven't done the numbers, but this may require more Delta-V than even an Orion can come up with.)