From the list, Mike Pence. Though Tim Pawlenty looks like another fellow who will appeal to most Republicans, too. Perhaps a few more than Pence, even.
If the economy is in horrible shape like it is now, I'd say Romney's stock rises.
Yes. If the economy continues to suffer the Republicans will not only want someone like Romney because of his business experience, but also would probably use the opportunity to trash left wing economics and Romney would be a much better candidate for that than Palin, Huckabee and others who mainly appeal to the social conservatives.