Amusingly, I'd set up something like NCR. "The Mojave Republic." It'd just be a competing nation to NCR to make sure neither nation grew too powerful. Basically, NCR needs a buffer state between it and the Wasteland beyond so it doesn't become an expansionist nutcase state. I imagine the King would be the President after the Courier's 2-4 terms. I would also do my best to offer peace terms to NCR in terms of electricity, water, and land which I'm going to make fertile with that Vault information. I would also point out the benefits of having a Securitron army next to the lands beyond to help as a defense against NCR's enemies. I'd also make an alliance with the Boomers just in case NCR gets some funny ideas.