I would probably make my own currency, you're thinking way too small, you would have so much more power than anybody in office. I would purchase some prime land and start my own city, I don't know where it would be located, but I would want it to be a major metropolis, and I would like it to be it's own country, maybe even enough for a few large cities. Again purchasing the land and forming another country on a mainland would be very tricky. Maybe I could purchase some land in the North Dakota border region.
But the goal would be to start an ideal society. To have an ethical place where people could live free, work together and happily, a society that would benefit honest people. It would be a very environmentally friendly society that would have reverse impact on the Earth. In a responsible culture, you don't need police, drugs, mental institutions, jails, etc. It would take much work, and it would have to be it's own country to start fresh.
That in turn would create a building block for societies to work towards. This would be a much bigger sphere of influence you could head if you were the richest person in the world.
I would also buy a brand new Chevy Lumina (sorry it's the baller in me)