Anyway... Not Florida and Virginia. I'd say Oklahoma, Louisiana, maybe Arkansas, maybe Mississippi and New Mexico, although the poverty in Mississippi would potentially be a drag on the new nation. Tennessee is just too far--no way would the government allow a new country to reach that deep into its heartland and partially sever the old US. The new country would also have to claim a fair chunk of the guld for the oil and such. A strong alliance with Alaska (hey, if Texas why not Alaska, its plenty big and far enough away) would also be good, allowing access to northern areas.
I agree about Alaska: it would be a natural fit for a new union. One thing to remember about poor states like Ole Miss: a lot of the poor are blacks who would be upset about secession because they want to live under a black Prez. Give them the option to load up their stuff and head on up north. They could repopulate Detroit, for example. Then whites in Mississippi would be left to join the new Union.
If multiple States secede from the U.S. and form a new association, they will not collectively constitute a new Nation. Each of the States is already a sovereign Nation unto itself.
The word State is synonymous with Nation. There is a reason they are not called something like "provinces".
The Pledge of Allegiance reference to "one nation [under God] indivisible" was put there as propaganda. It was a post-Lincoln concept.