I would do what a lot of billionaires are doing, starting my own space travel company. I would have a space station way bigger than the international space station that was capable of leaving low earth orbit and hope to be able to get it built and moved to lunar orbit before I die. With unlimited cash I would be limited by the availability of smart capable motivated people. If enough of the right people could be found I would work on a self-sustaining lunar colony as well. I would hire Elon to do my launches and help him grow his business and maybe he will then be able to make progress on his goal of a Mars colony.
Tim